Liquid-crystal switching elements comprising a liquid-crystal layer which has extremely low optical retardation and liquid-crystal displays containing them

ABSTRACT

The present invention relates to a liquid crystal electro-optical switching member that comprises at least one polariser and a liquid crystal layer having an initial orientation in which the liquid crystal molecules are oriented so as to be essentially parallel to the substrates and to each other. The change of orientation of the liquid crystals, from their initial orientation that is substantially parallel to the substrates, is induced by a corresponding electric field which is oriented so as to be practically parallel to the substrates in the case liquid crystal with a negative dielectric anisotropy and so as to be practically perpendicular to the substrates in the case liquid crystal with a positive dielectric anisotropy. The liquid crystal layer has an optical delay [(d Δn ) LC?] of between 0.06 and 0.43 μm. The present invention also relates to a liquid crystal display system that comprises said liquid crystal switching members.

The invention relates to an electro-optical liquid-crystal switchingelement comprising at least one polariser and a liquid-crystal layerwhich has an initial alignment in which the liquid-crystal molecules arealigned essentially parallel to the substrates and essentially parallelto one another, in which the realignment of the liquid crystals fromtheir initial alignment essentially parallel to the substrates is causedby a corresponding electric field, which, in the case of liquid-crystalmaterials of negative dielectric anisotropy, is aligned essentiallyparallel to the substrates and, in the case of liquid-crystal materialsof positive dielectric anisotropy, is aligned essentially perpendicularto the substrates, where the liquid-crystal layer has an extremely lowoptical retardation d-An in the range from 0.06 μm to 0.43 μm, and theliquid-crystal switching element preferably contains, in addition to theliquid-crystal layer, a further birefringent layer, preferably a λ/4layer or two λ/4 layers or a λ/2 layer, and 2 liquid-crystal displaysystems containing liquid-crystal switching elements of this type.

The present invention furthermore relates to liquid-crystal media, inparticular of low birefringence, for use in the liquid-crystal displaysystems. These liquid-crystal display systems containing theliquid-crystal switching elements are, inter alia, display screens oftelevision sets, computers, such as, for example, notebook computers ordesktop computers, central control units and of other equipment, forexample gambling machines, electro-optical displays, such as displays ofwatches, pocket calculators, electronic (pocket) games, portable databanks, such as PDAs (personal digital assistants) or of mobiletelephones.

In particular, the liquid-crystal display systems according to theinvention are highly suitable for applications with display of greyshades, such as, for example, television sets, computer monitors andmultimedia equipment. Both mains-independent operation and alsooperation on the mains are possible here. Mains operation is oftenpreferred.

These liquid-crystal display devices are also known as liquid-crystaldisplays.

The liquid-crystal switching elements typically used in theliquid-crystal display devices of this type are the known TN (twistednematic) switching elements, for example in accordance with Schadt, M.and Helfrich, W. Appl. Phys. Lett. 18, pp. 127 ff (1974) and inparticular in their special form with low optical retardation d·Δn inthe range from 150 nm to 600 nm in accordance with DE 30 22 818, STN(super twisted nematic) switching elements, such as, for example, inaccordance with GB 2.123.163, Waters, C. M., Brimmel, V, and Raynes, E.Pproc. 3^(rd) Int. Display Research Conference, Kobe 1983, pp. 396 ffand Proc. SID 25/4, pp. 261 ff, 1984, Scheffer, T. J. and Nehring, J.Appl. Phys. Lett. 45, pp. 1021 ff, 1984 and J. Appl. Phys. 58, pp. 3022ff, 1985, DE 34 31 871, DE 36 08 911 and EP 0 260 450, IPS (in-planeswitching) switching elements, as described, for example, in DE 40 00451 and EP 0 588 568, and VAN (vertically aligned nematic) switchingelements, as described, for example, in Tanaka, Y. et al. Taniguchi, Y.,Sasaki, T., Takeda, A., Koibe, Y., and Okamoto, K. SID 99 Digest pp. 206ff (1999), Koma, N., Noritake, K., Kawabe, M., and Yoneda, K.,International Display Workshop (IDW) '97 pp. 789 ff (1997) and Kim, K.H., Lee, K., Park, S. B., Song, J. K., Kim, S., and Suk, J. H., AsiaDisplay 98, pp. 383 ff, (1998).

In these liquid-crystal display devices which were known hitherto andare for the most part already commercially available, the opticalappearance is inadequate, at least for demanding applications. Inparticular the contrast, especially in the case of coloured displays,the brightness, the colour saturation and the viewing-angle dependenceof these parameters are in clear need of improvement and have to beimproved if the display devices are to compete with the performancefeatures of the widespread CRTs (cathode ray tubes). Furtherdisadvantages of the liquid-crystal display devices are often their poorspatial resolution and inadequate response times, in particular in thecase of STN switching elements, but also in the case of TN switchingelements or IPS (“in-plane switching”) and VAN (vertically alignednematic”) switching elements, in the case of the latter especially ifthey are to be used for the reproduction of video, such as, for example,in multimedia applications on computer display screens or in the case oftelevision sets. Particularly for this purpose, but also even for thedisplay of rapid cursor movements, short response times, preferably ofless than 32 ms, particularly preferably of less than 16 ms, aredesired.

The requirements regarding the viewing-angle dependence of the contrastare highly dependent on the application of the display devices. Thus,for example, the horizontal viewing-angle range is the most important intelevision screens and computer monitors, whereas centrosymmetrical orat least approximately centrosymmetrical viewing-angle distributions aredesired in other applications. Displays having virtuallycentrosymmetrical viewing-angle distributions are required, inparticular, in projection displays in order to utilise the opticalapertures as well as possible, but also in computer display screenshaving a swivel base. These display screens allow the display to betilted through 90° in order to change from portrait mode to landscapemode while retaining the resolution of the display. Displays of thistype obviously have to have similar horizontal and verticalviewing-angle ranges since these are interchanged on tilting.

In general, it should be noted that for practical acceptance of adisplay, it is not primarily its contrast or its maximum contrast ratiothat is crucial, but instead the viewing-angle dependence of thecontrast is frequently important. However, these properties should beweighted differently depending on the application.

TN switching elements having a d·Δn in the range from 0.2 μm to 0.6 μm,as described in DE 30 22 818, generally have very good colour saturationand colour depth, but an inadequate viewing angle for demandingapplications, such as, for example, desktop computer monitors.

In some embodiments, such as, for example, in typical IPS displaydevices, the brightness of the display can be achieved to an inadequateextent or can only be achieved at great expense with backlighting. Incontrast, VANs are frequently characterised by inadequate coloursaturation and colour depth, and furthermore the production of VANs iscomplex owing to the homeotropic alignment, which is difficult toachieve, and owing to the long filling times.

EP 0 264 667 describes TN cells having twist angles (φ, known as twistfor short) in the range from 100 to 80° with a d·Δn in the range from0.2 μm to 0.7 μm. Although these have both an improved viewing-angledependence of the contrast and lower steepness of the electro-opticalcharacteristic line compared with TN cells having a 90° twist, theyhave, however, significant disadvantages. Thus, inter alia, theirbrightness and their contrast are significantly lower than those ofconventional TN switching elements. In addition, the TN switchingelements in accordance with EP 0 264 667 switch relatively slowly.

Raynes, E. P., Mol. Cryst. Liq. Cryst. 4, p. 1, ff, 1986, describes thevoltage dependence of the tilt angle in the centre of the liquid-crystallayer (φ_(M), also known as mid-plane tilt angle or mid-plane tilt forshort) as a function of the addressing voltage for cells containing anematic liquid crystal with a tilted alignment having a tilt angle offrom 0° to 270°.

DE 40 10 503 and WO 92/17831, which corresponds thereto, describe, interalia, TN switching elements having twist angles in the range fromgreater than 0° to 90° which contain one or more compensation layers,where the compensation layers for compensation of the optical pathdifference of the switching cell have the same optical retardation asthe switching cell. In cells having a twist angle regarded as small, forexample 22.5°, the compensation layer may also be omitted. However, theswitch elements described in this publication have, in particular,inadequate contrast, which is frequently accompanied by a stillconsiderable viewing-angle dependence of the contrast. Furthermore, theresponse times, in particular those for the addressing of grey shades,are usually inadequate.

DE 42 12 744 proposes improving the viewing-angle dependence of thecontrast and in particular the display of grey shades by TN cells havinga 90° twist and a d·Δn in the range from 0.15 μm to 0.70 μm by using acholesteric liquid-crystal material having a small cholesteric pitch (P)with a d/P ratio in the range from 0.1 to 0.5. The TN switching elementsof DE 42 12 744 exhibit similar disadvantages to the switching elementsdescribed in EP 0 264 667. The saturation voltage also increasessignificantly in the cells in accordance with DE 42 12 744 compared withconventional TN cells, albeit not so highly pronounced as in the TNswitching elements of EP 0 264 667.

WO 91/06889 and the corresponding U.S. Pat. No. 5,319,478 describe[lacuna] the minimum optical retardations of λ/2 or λ/4 and proposetheir operation with circular-polarised light. Cells having a twistedstructure of the liquid crystal are preferred.

Van Haaren et al., Phys. Rev. E, Vol. 53, No. 2, pp. 1701 to 1713,investigates the elastic constants for surface coupling (k₁₃) of thenematic liquid-crystal mixture ZLI-4792, Merck KGaA, in an untwistedcell with a planar alignment having a λ/4 plate.

Tillin et al., SID 98 Digest, pp. 311-314 (1998), investigatesreflective liquid-crystal switching elements having a single polariser.He mentions, inter alia, a liquid-crystal switching element having anuntwisted liquid crystal which switches from a (d·Δn/λ) of ½ to ¼ innormally white mode and from ¼ to 0 in normally black mode. However, thepublication prefers liquid-crystal layers having a twisted structure. Inaddition, liquid-crystal cells having an (d·Δn/λ) of ⅓ containing abirefringent layer having a (d·Δn/λ) of ½ and optionally an additionalbirefringent layer having a (d·Δn/λ) of {fraction (4/55)} are presented.In these, the characteristic directions of the optical components formangles to one another which differ by 0° and 90°. The switching elementshaving birefringent layers which are described here have a complexstructure and are consequently not easy to produce. In addition, thebrightness is not particularly good, in particular in the switchingelements having a plurality of birefringent layers.

It has now been found that the liquid-crystal switching elementsaccording to the present invention do not have the disadvantages of theknown switching elements or at least do so to a significantly reducedextent. They are characterised by very good contrast at the same time asexcellent viewing-angle dependence of the contrast. They allow thedisplay both of grey shades and of half-tone colours over a broad rangeof observation angles. In addition, the response times are good and inparticular are adequate for video reproduction.

The liquid-crystal switching elements according to the present inventioncontain a liquid-crystal layer having a small optical retardation and,if desired, a further birefringent layer, preferably a λ/4 layer, a λ/2layer or two λ/4 layers, and at least one polariser. The two λ/4 layersmay replace the λ/2 layer.

The transmissive or transflective liquid-crystal switching elementsaccording to the present invention preferably contain a polariser and ananalyser, which are arranged on opposite sides of the arrangement ofliquid-crystal layer and birefringent layer. Polariser and analyser arejointly referred to as polarisers in this application.

FIG. 1 shows a diagrammatic view of the principle of construction of aliquid-crystal switching element according to the invention in thepreferred embodiment of a transmissive switching element having a lightsource, a having a liquid-crystal layer, having two polarisers, having abirefringent layer (here, as preferred, a λ/4 layer) and having crossedpolarisers.

FIG. 1a is a side view. For reasons of clarity, the substrates of theliquid-crystal cell between which the liquid-crystal layer is locatedand the electrode layers located on the alignment layers present on theinsides of the substrate and on one or both substrates are omitted. Eachof the two polarisers is located on one of the two sides of theliquid-crystal cell. The birefringent layer is located between theliquid-crystal cell and one of the two polarisers, preferably, as shown,on the side facing away from the light source, i.e. between theliquid-crystal cell and the analyser. In this configuration, the fastaxis of the birefringent layer is parallel to the transmission axis ofthe polariser. The light from the light source (backlighting, BL forshort) thus passes successively through the polariser, theliquid-crystal cell, the birefringent layer and the analyser beforereaching the observer (not shown). However, it is also possible toreverse the sequence of liquid-crystal layer and birefringent layer. Inthis case, however, the relative alignment of these two components alsohas to be changed. The fast axis of the birefringent layer is thenpreferably at an angle of 45° to the polariser, and the projection ofthe alignment of the liquid crystal in the centre of the cell betweenthe substrates is preferably parallel to the transmission direction ofthe polariser.

FIG. 1b shows a plan view, i.e. along the z-axis in FIG. 1a. It showsthe alignment of the relevant axes of the individual optical componentsto one another and defines the corresponding angles. The symbols fromFIG. 1a are used where appropriate. Ψ_(PP) denotes the angle between thetransmission axes of the two polarisers (here 90°), Ψ_(PL) denotes theangle between the transmission axis of the polariser and thepreferential direction of the liquid-crystal director in the centre ofthe layer between the substrates (n_(∥)) (here 45°). The fast axis ofthe λ/4 layer is parallel to the transmission axis of the polariser. Theangle Ψ_(PD) is thus 0°. Finally, the observation angle in the plane ofthe switching element (Φ) is indicated with examples of 0°, 90°, 180°and 270°.

The observation angles in the plane of the display (Φ and Φ′) andperpendicular to the normal (Θ) are defined in FIG. 2. The observationangles Φ′ commence with Φ′=0° in the quadrant with the highest contrastat the angle of the highest contrast, which is generally in thedirection of n_(∥). Thus, [lacuna] or Φ′ is shifted by 45° compared withΦ.

The fast axis of the λ/4 layer is parallel to the transmission directionof the polariser, to that of the polariser adjacent to the λ/14 layer inthe case of the presence of two or more polarisers (cf. FIG. 1b). Ananalogous situation applies in the presence of two λ/4 layers or of oneλ/2 layer.

Linear polarisers are preferably used in the switching elementsaccording to the present application. These linear polarisers may besingle-layered polarisers or consist of a combination of a plurality oflayers, where these layers may also comprise two or more polarisinglayers. The degree of polarisation of the polarisers is chosen to besufficiently high in order to achieve good contrast, but alsosufficiently low to achieve good brightness of the switching element.The use of a polariser having a relatively low degree of polarisation, aso-called clean-up polariser, in combination with a polariser having arelatively high degree of polarisation often proves advantageous. Inthis case, the polarisers are preferably bonded using an adhesive ofappropriate refractive index in order to avoid light losses at thesurfaces.

The liquid-crystal layer is usually held between two substrates. Atleast one of the substrates transmits light, preferably both substratestransmit light. The light-transmitting substrates consist, for example,of glass, quartz glass, quartz or of transparent plastics, preferably ofglass and particularly preferably of borosilicate glass.

The substrates together with an adhesive frame form a cell in which theliquid-crystal material of the liquid-crystal layer is held. Thesubstrates are preferably planar.

The separation of the planar substrates is kept essentially constantover the entire area by means of spacers. These spacers may be used onlyin the adhesive frame or, alternatively, distributed over the entirearea of the cell. The use of spacers exclusively in the adhesive framereduces problems with misalignment in the liquid-crystal layer. It isparticularly appropriate in the case of liquid-crystal cells havingsmall area diagonals, in particular up to 5″ and preferably up to 3″. Inthe case of larger-area liquid-crystal cells, in particular in the caseof those having diagonals of 14″ or more and very particularly of 18″ ormore, spacers are preferably employed distributed over the entire area.In this case, it is possible and often advantageous to employ differentspacers in the adhesive frame and in the cell area. The preferred limitsfor the various distributions of the spacers over the cell areaadditionally depend on the thickness of the substrates used. Thus, theuse of spacers distributed over the entire display area is preferred inthe case of relatively thin glass and in the case of relatively largediagonals.

The preferred substrate thicknesses are from 0.3 mm to 1.1 mm,particularly preferably from 0.4 mm to 0.7 mm. In the case of therelatively large diagonals of the cells, the substrates of relativelylarge thicknesses are preferably employed.

The liquid-crystal switching elements according to the invention aredistinguished by very good grey-shade capacity, a low dependence of thecontrast on the observation angle, even in the case of colour display,with a large viewing-angle range and low contrast inversion and, inparticular, by very short response times. In particular, the inversecontrast, as defined, for example, in DE 42 12 744, which occurs, forexample, in displays in accordance with DE 30 22 818, is significantlyreduced, in particular at relatively large observation angles θ.

As spacers, commercially available spacers in bead form or incylindrical form may consist either of plastics or of inorganicmaterials, such as, for example, chopped glass fibre. Suitable spacersare furthermore more or less regular, raised structures on, preferably,one of the substrates. These regular, raised structures may have variousshapes, such as, for example, rectangular, square, oval or round columnsor pyramid shafts, but also strip- or wave-shaped structures.

The liquid-crystal switching elements in accordance with the presentapplication have, if they are reflective switching elements, at leastone polariser and a reflector, with at least one polariser and thereflector being located on opposite sides (i.e. substrates) to oneanother in the liquid-crystal cell. In the case that they aretransmissive or reflective switching elements, these have at least twopolarisers, in each case at least one of which is arranged on one of thetwo opposite sides of the liquid-crystal cell (so-called sandwichstructure). The obligatory polarisers mentioned are preferably linearpolarisers and particularly linear polarisers having a high degree ofpolarisation.

In addition to the obligatory polarisers, the switching elementsaccording to the invention may contain one or more further polarisers.These may be so-called clean-up polarisers having a lower degree ofpolarisation, but high transmission. In particular in the case ofreflective switching elements, however, a further polariser having ahigh degree of polarisation may also be present. This is preferablyarranged between the liquid-crystal cell and the reflector. However, theuse of additional polarisers is generally less preferred since in mostcases it results in a reduction in the transmission. However, it isusual, in particular in connection with so-called brightness-increasingcomponents, which may, for example, contain cholesteric polymer films.

In the case of transmissive and transflective displays in accordancewith the present application, the two obligatory polarisers are arrangedeither crossed or parallel to one another. In this application, thedirections of the arrangement of the polarisers are relative to theirabsorption axes. The crossed arrangement of the polarisers is preferred.The angle of the absorption axes to one another (Ψ_(PP)) in the case ofcrossed polarisers is in the range from 75° to 105°, preferably from 85°to 95°, particularly preferably from 88° to 92°, especially preferablyfrom 89° to 91° and very particularly preferably 90°, and in the case ofparallel polarisers is from −15° to 15°, preferably from −5° to 5°,particularly preferably from −2° to 2°, especially preferably from −1°to 1° and very particularly preferably 0°.

The angle between the absorption axis of the polariser adjacent to theliquid-crystal layer with the direction of the alignment of the directorof the liquid-crystal material in the unswitched (field-free) state atthe adjacent substrate (Ψ_(PL)) is from 35° to 55°, preferably from 40°to 50°, particularly preferably from 43° to 47°, in particular from 44°to 46° and ideally 45°. This applies to the untwisted alignment of theliquid crystal. In the case of the twisted alignment of the liquidcrystal, the preferential direction for the indication of the angleΨ_(PL) is the projection of the alignment of the liquid-crystal directorin the centre between the two substrates of the cell on the substrateadjacent to the polariser. On use of further birefringent layers and/orcompensators in addition to the obligatory or preferred λ/4 or λ/2 layeror layers, depending on the embodiment, other angles between thepolariser direction and the liquid-crystal alignment can also beemployed. However, these are generally not preferred.

The twist angle (φ) of the liquid-crystal layer between the twosubstrates is, in particular in the case of switching elements having abirefringent layer, in particular having a λ/4 or λ/2 layer, or having aplurality of birefringent layers, in particular having two λ/4 layers,preferably from −20° to 20°, particularly preferably from −10° to 10°,especially preferably from −5° to 5°, very particularly preferably from−2° to 2° and most preferably from −1° to 1°.

For the preferred embodiment without a birefringent layer, i.e. withouta λ/4 or λ/2 layer or layers, the liquid-crystal layer is essentiallyuntwisted and particularly preferably untwisted. A twist angle (φ) offrom −6° to 6° is preferred. The twist angle is particularly preferablyfrom −1.0° to 1.0°, very particularly preferably from −0.5 to 0.5,especially preferably 0.0°.

The liquid-crystal materials are aligned at the substrate surfaces byconventional methods. To this end, use can be made of inclined vapourdeposition with inorganic compounds, preferably oxides, such as SiO_(x),alignment on surfaces that have been subjected to antiparallel rubbing,in particular on polymer layers, such as polyimide layers, that havebeen subjected to antiparallel rubbing, or alignment on photopolymerisedanisotropic polymers. In the case of vertical alignment (abbreviated toVA), it is also possible to employ lecithin or surface-active substancesfor homeotropic alignment.

The liquid-crystal switching elements in accordance with the presentinvention can be produced using the production processes in theproduction plants for the most widespread liquid-crystal switchingelements to date, the TN liquid-crystal switching elements. Inparticular, there is no need for special effort regarding alignment ofthe liquid-crystal director, as, for example, in STN (high tilt angle)or in VAN (homeotropic alignment). In addition, in contrast to TN, IPShaving a twisted initial state and in particular to STN, additives, suchas chiral dopants, can be substantially and frequently even completelyomitted. A further process parameter which is sometimes difficult tocontrol is thus superfluous.

The surface tilt angle at the substrates (φ₀, tilt for short) is in therange from 0° to'15°, preferably in the range from 0° to 10°,particularly preferably in the range from 0.1° to 5° and especiallypreferably in the range from 0.2° to 5° and most preferably in the rangefrom 0.3° to 3°. The surface tilt angle at the alignment layer on atleast one of the substrate surfaces is from 0.5° to 3°. The tilt angleat the two substrates is preferably essentially identical.

The electrodes on the substrates transmit light, at least on one of thesubstrates and preferably on both substrates. The material employed forthe electrodes is preferably indium tin oxide (ITO), but it is alsopossible to use aluminium, copper, silver, and/or gold.

Since the surface tilt angle in the liquid-crystal display elementsaccording to the invention may be small, the use of anisotropicallyphotopolymerisable materials, such as, for example, cinnamic acidderivatives, the so-called photoalignment should particularlyadvantageously be employed.

This applies in particular to a preferred embodiment of theliquid-crystal display elements according to the invention, theembodiment with multidomain switching elements. In these, the individualliquid-crystal switching elements or their individual display electrodes(also known as pixels) are divided into sub-areas of different alignmentof the liquid-crystal director, at least in the switched state, butgenerally also in the unswitched state, so-called domains. These domainshaving different alignment in the switched state can be induced, forexample, by different surface tilt angles or by different differentialalignment on the substrates. However, they can also be induced bycorresponding electric fields with a sufficiently inclined alignment,for example through slotted electrodes, or through non-planar surfacetopographies. In particular in the case of induction of the domains byelectric fields which are not perpendicular to the substrates, but alsoin the case of non-planar surface topographies, the smallest possiblesurface tilt angle, if possible of 0°, is usually preferred, as canreadily be achieved by means of photoalignment. The individual pixels ofthe multidomain switching elements preferably contain two or more,preferably precisely a multiple of two, very particularly preferably twoor four, domains. The tilt angles of the liquid-crystal director in thecentre of the liquid-crystal layer (φ_(M), mid-plane tilt angle) ofthese domains in the switched state are preferably opposite one anotherin pairs. The result of this is that the viewing-angle dependencies ofthe domains, also known as sub-pixels, cancel each other out, and theundesired effect is eliminated. The light-scattering disclinations whichoccur at the domain limits are covered by a corresponding mask,preferably a black mask, in order to improve the contrast. Throughappropriate design of the structure or structures inducing the domains,and of the mask, the restriction in the light yield by the reducedaperture ratio can be kept as low as possible.

The larger of the preferred surface tilt angles are particularlyadvantageous for a definition of the preferred quadrant, i.e. thequadrant in which the best contrast is observed. They result, inparticular, in a suppression of reverse tilt domains, which ariseparticularly easily on application of nonorthogonal fields.

Active electric switching elements of the active matrix which are usedare both bipolar structures, such as diodes, for example MIM diodes orback to back diodes, if desired with reset, and tripolar structures,such as transistors, for example thin-film transistors (TFTs), orvaristors. For the liquid-crystal display devices in accordance with thepresent application, TFTs are preferred. The active semiconductor mediumof these TFTs is amorphous silicon (a-Si), polycrystalline silicon(poly-Si) or cadmium selenide (CdSe), preferably a-Si or poly-Si.Poly-Si here equally denotes high-temperature and low-temperaturepoly-Si.

In liquid-crystal switching elements according to a preferred embodimentof the present invention, the liquid-crystal layer preferably has anoptical retardation (d·Δn) of from 0.14 μm to 0.42 μm, particularlypreferably from 0.22 μm to 0.34 μm, especially preferably from 0.25 μmto 0.31 μm, very particularly preferably from 0.27 μm to 0.29 μm andideally 0.28 μm.

To this end, liquid-crystal materials of low birefringence Δn arepreferably employed. The birefringence of the liquid-crystal materialsis preferably from 0.02 to 0.09, particularly preferably from 0.04 to0.08, especially preferably from 0.05 to 0.075, very particularlypreferably from 0.055 to 0.070 and ideally from about 0.060 to 0.065.

The layer thickness of the liquid-crystal layer is preferably from 1 μmto 10 μm, preferably from 2 μm to 7 μm, particularly preferably from 3μm to 6 μm and especially preferably from 4 μm to 5 μm.

In liquid-crystal display devices containing liquid-crystal cells havinga diagonal of up to 6″, layer thicknesses of the liquid-crystal layer offrom 1 μm to 4 μm and particularly from 2 μm to 3 μm are preferred. Inliquid-crystal display devices containing liquid-crystal cells having adiagonal from 10″, layer thicknesses of the liquid-crystal layer of from3 μm to 6 μm and particularly from 4 μm to 5 μm are preferred.

There are two different preferred sub-forms for this preferredembodiment. In the first of these preferred sub-embodiments of thepresent invention, the liquid-crystal layer has an optical retardation(d·Δn) of from 0.20 μm to 0.37 μm, preferably from 0.25 μm to 0.32 μm,particularly preferably from 0.26 μm to 0.30 μm, very particularlypreferably from 0.27 μm to 0.29 μm, and most preferably 0.28 μm.

In this preferred sub-embodiment, the display element surprisingly doesnot require a λ/4 layer in some applications. It is neverthelesscharacterised by good brightness, excellent contrast and excellentviewing-angle dependence and very good grey-shade and colour-shadedisplay given an appropriate polariser setting, preferably at an angleof essentially 45° to the liquid-crystal preferential direction. Withouta λ/4 layer, a very broad viewing-angle range for the observation angleΘ is achieved, although not for all observation angles Φ. By contrast,the viewing-angle range in the switching elements having a λ/4 layer issignificantly more centrosymmetrical, i.e. extends to all similar, largevalues of the observation angle Θ at all observation angles Φ (cf. inthis respect also FIGS. 9a) and 9 b) regarding Examples 1 and 2).

In the second of these preferred sub-embodiments of the presentinvention, the display elements preferably contain a λ/4 layer, and theliquid-crystal layer has an optical retardation [(d·Δn)_(LC)] of from0.10 μm to 0.45 μm, preferably from 0.20 μm to 0.37 μm, particularlypreferably from 0.25 μm to 0.32 μm, very particularly preferably from0.26 μm to 0.30 μm, especially particularly preferably from 0.27 μm to0.29 μm, and most preferably 0.28 μm. The liquid-crystal layer in theunswitched state thus behaves approximately like a λ/2 layer. Preferenceis furthermore given here to an embodiment in which the (d·Δn)_(LC) isdifferent from 0.28 μm, preferably in the range from 0.10 μm to 0.27 μmor from 0.30 μm to 0.45 μm, particularly preferably from 0.14 μm to 0.25μm or from 0.32 μm to 0.42 μm, very particularly preferably from 0.22 μmto 0.25 μm, or from 0.32 μm to 0.34 μm.

In the present application, the wavelength x always preferably relatesto the wavelength of maximum sensitivity of the human eye, to 554 nm,unless explicitly stated otherwise.

The terms λ/4 layer and λ/4 plate, or λ/2 layer and λ/2 plate aregenerally used with equal importance in the present application. Theterm λ in λ/4 layer and λ/2 layer denotes a wavelength in the region ofλ±30%, preferably λ±20%, particularly preferably λ±10%, especiallypreferably λ±5% and very particularly preferably λ±2%. The wavelengthhere, unless stated otherwise, is 554 nm. The wavelength of the λ/4layer or λ/2 layer is generally and in particular in the case of asignificant spectral distribution given as the central wavelengththereof.

The λ/4 layer or λ/2 layer is an inorganic layer or preferably anorganic layer, for example comprising a birefringent polymer, forexample stretched films (PET) or liquid-crystalline polymers.

The use particularly of the smaller of the preferred layer thicknessesof the liquid-crystal layer is preferred in view of the advantageousshort response times which can be achieved thereby. In addition, ittends to allow the use of conventional liquid-crystal materials or makesat least lower demands regarding the often difficult implementation ofthe small an values.

By contrast, the use of liquid-crystal materials having a particularlysmall Δn is preferred in view of the lower layer thickness dependence ofthe contrast and of the background hue of the liquid-crystal switchingelements. In addition, the production of the display elements in thisembodiment is possible with significantly greater yields, especially inthe case of liquid-crystal cells having larger diagonals.

For a broad working-temperature range, particular preference is given toliquid-crystal materials having a relatively high clearing point, sincethe effect of the λ/4 layer is significantly temperature-dependent,owing to the temperature dependence of the birefringence of theliquid-crystal materials [Δn_(LC)(T)], and Δn_(LC)(T) in liquid-crystalmaterials having a high clearing point is relatively low. Thetemperature dependence of the optical arrangement as a whole is thuskept relatively low and can thus, if necessary, also be compensated morereadily.

In a second preferred embodiment of the present invention, theliquid-crystal layer has an optical retardation of from 0.07 μm to 0.21μm, preferably from 0.11 μm to 0.17 μm, particularly preferably from0.12 μm to 0.16 μm, especially preferably from 0.13 μm to 0.15 μm andvery particularly preferably 0.14 μm. In this preferred embodiment, thedisplay element preferably has at least one birefringent layer,preferably a λ/2 layer or two λ/4 layers, in addition to theliquid-crystal layer.

To this end, liquid-crystal materials of low birefringence Δn are againpreferably employed. The birefringence of the liquid-crystal materialsis preferably from 0.02 to 0.09, particularly preferably from 0.04 to0.08, especially preferably from 0.05 to 0.07, very particularlypreferably from 0.055 to 0.065 and ideally about 0.060.

The layer thickness of the liquid-crystal layer is preferably from 0.5μm to 7 μm, preferably from 1 μm to 5 μm, particularly preferably from1.5 μm to 4 μm and especially preferably from 2 μm to 2.5 μm. Particularpreference is given here to displays containing liquid-crystal cellshaving smaller diagonals, in particular in the range from 0.5″ to 6″,particularly in the range from 1″to4″.

In this second preferred embodiment, the liquid-crystal switchingelements preferably contain two λ/4 layers or, particularly preferably,one λ/2 layer. The two λ/4 layers can be used on different sides of theliquid-crystal layer, but they can also be located on the same side ofthe liquid-crystal layer.

In particular if the optical retardation of the liquid-crystal layer[(d·Δn)_(LC)] is significantly different from 0.14 μm, particularly ifit is in the range from 0.07 μm to 0.12 μm or from 0.16 μm to 0.21 μm,the use of two λ/4 layers, or one λ/2 layer is necessary.

This second preferred embodiment makes high demands both regarding thebirefringence of the liquid-crystal material and regarding the layerthickness of the liquid-crystal layer. However, the requirements of thelayer thickness of the liquid-crystal layer are somewhat reduced by thelower layer-thickness dependence of the optical properties of theswitching elements. In the case of small-area liquid-crystal cells, thelayer-thickness tolerance is in addition easier to comply with. Inaddition, the thin liquid-crystal cells in this preferred embodimenthave extremely short short response times.

The liquid-crystal switching elements in accordance with the presentapplication can be operated transmissively, transflectively orreflectively. The transmissive or transflective mode, particularlypreferably the transmissive mode, is preferred.

Transflective displays enable the advantages of low power consumption ofthe reflective displays to be combined with that of good legibility atlow ambient brightness of the transmissive displays with backlighting.

Reflectors which can be used are dielectric or metallic layers. Metallicreflector layers are preferred. On use of metallic reflectors, a greaterby, variation in the optical retardation of the liquid-crystal layer canbe tolerated. If a dielectric mirror is used, the optical retardation ofthe liquid-crystal layer is essentially λ/4, in particular in the caseof switching elements without a birefringent layer. On use of a secondlinear polariser between the liquid-crystal layer and the reflector,preference is given to a dielectric reflector, which preferably has alow fraction of depolarised reflection.

Particularly preferred combinations of the optical retardation of theliquid-crystal layer and of the birefringent layer are shown in thefollowing table (Table 1). In this table, the preferred settings of thepolarisers both with respect to one another and with respect to thepreferential direction of the liquid crystals are also indicated.

TABLE 1 Preferred parameter combinations A) Transmissive ortransflective switching element (dΔn)_(LC)/ Birefringent Ψ_(PP)/°Ψ_(PL)/° μm layer Preferably Preferably 0.220 to λ/4 plate 0 to 10 90 to70 45 +/− 10 45 +/− 5 0.276 obligatory 0.277 λ/4 plate 0 +/− 5 90 +/− 545 +/− 10 45 +/− 5 preferred 0.278 to λ/4 plate 0 to 15 90 to 110 45 +/−10 45 +/− 5 0.335 obligatory 0.110 to λ/2 plate 0 to 15 90 to 70 45 +/−10 45 +/− 5 0.138 obligatory 0.1385 λ/2 plate 0 +/− 5 90 +/− 5 45 +/− 1045 +/− 5 preferred 0.139 to λ/2 plate 0 to 15 90 to 110 45 +/− 10 45 +/−5 0.168 obligatory B) Reflective switching element having two polarisersΨ_(PL)/° (dΔn)_(LC)/μm Birefringent layer Ψ_(PP)/° preferably 0.110 to0.138 λ/4 plate 90 to 70 45 +/− 5 obligatory 0.1385 +/− λ/4 plate 90 +/−5 45 +/− 5 0.0004 preferred 0.139 to 0.168 λ/4 plate 90 to 110 45 +/− 5obligatory C) Reflective switching element having one polariser(dΔn)_(LC)/μm Birefringent layer Ψ_(PL)/° 0.110 to 0.138 λ/4 plate 45+/− 5 obligatory 0.1385 +/− λ/4 plate 45 +/− 5 0.0004 preferred 0.139 to0.168 λ/4 plate 45 +/− 5 obligatory Note: the term λ/2 plate in theabove table expressly also covers two λ/4 plates.

The angle Ψ_(PD) is preferably 0°+/−5°, particularly preferably 0°+/−2°and very particularly preferably 0°+/−1°.

The following table (Table 2) shows preferred combinations of theoptical retardations of the liquid-crystal layer and, if present, of thebirefringent layer with the twist angles of the liquid-crystal layer.

TABLE 2 Preferred parameter combinations A) Transmissive ortransflective switching element having a birefringent layer φ/° (d ·Δn)_(LC) (d · Δn)_(DS) Preferably Part. pref. λ/2 λ/4 0 +/− 20 0 +/− 8 0+/− 4 λ/4 λ/2 0 +/− 20 0 +/− 8 0 +/− 4 λ/4 2 * (λ/4) 0 +/− 20 0 +/− 8 0+/− 4 B) Transmissive or transflective switching element with nobirefringent layer (d · Δn)_(LC)/λ φ/° Unswitched Switched PreferablyPart. pref. 1/2 0 0 +/− 6 0 +/− 0.5 0 +/− 0.3 1/4 0 0 +/− 6 0 +/− 0.5 0+/− 0.3

The liquid-crystal switching elements in accordance with the presentinvention act as light valves on application of a voltage. This isshown, for example, in FIGS. 1 and 2 for the liquid-crystal switchingelements of the first preferred embodiment of the present application.With crossed polarisers, the switching element in the voltage-freestate, the “off state”, transmits light (known as “normally white” oralternatively positive contrast). With increasing applied voltage, athreshold is initially reached from which the transmission begins todrop. The transmission then drops in a virtually linear manner withincreasing voltage over a relatively broad voltage range. At highervoltage, the transmission comes up against a limit, and saturation isreached.

The liquid-crystal switching elements are preferably addressed in such away that the optical retardation of the liquid-crystal layer in the caseof complete switching approaches 0 nm or at least essentially 0 nm. Thisnaturally does not exclude the addressing of grey shades with theintermediate values required for this purpose.

It goes without saying that in order further to improve the opticalproperties, the display elements in accordance with the presentinvention may contain further optical layers. These layers can be, forexample, compensation layers, which are employed, in particular, indisplay elements having a twist of the liquid-crystal layer which isdifferent from 0°, or alternatively films which collimate the light, forexample from backlighting, such as the so-called “brightness enhancementfilms” (BEF) or cholesteric circular polarisers for utilisation of thehalf of the backlighting light which is otherwise absorbed by thepolariser.

The display of coloured images using the display elements in accordancewith the present invention is possible in various ways. Backlightinghaving an approximately white spectral distribution is preferably used,and the colour splitting carried out by a colour filter. The individualliquid-crystal switching elements are then employed as light valves forthe respective primary colours. The backlighting can also be matched tothe spectral characteristics of the colour filter in such a way that ithas corresponding intensity maxima in the respective transmissionregions. However, colour display can also be achieved by birefringenceeffects.

The liquid-crystal switching elements according to the invention and inparticular the reflective switching elements preferably operate innormally white mode (for the polariser setting, cf. FIG. 3 and theassociated description).

Liquid-crystal mixtures which are used in the liquid-crystal switchingelements according to the invention preferably comprise from 3 to 27,particularly preferably from 10 to 21 and very particularly preferablyfrom 12 to 18, individual compounds. The individual compounds preferablyemployed preferably each contain a 1.4′-trans-trans-bicyclohexylene unitof the sub-formula i:

where

Z is a single bond, —CH₂CH₂— or —CF₂CF2 and

n is 1 or 2.

It is also possible here for one or preferably two non-adjacent —CH₂—groups in one of the cyclohexane rings to be replaced by oxygen atoms orfor two adjacent —CH₂— groups to be replaced by one —CH═CH— group.

In the case of compounds having a total of only two six-membered rings,it is also possible, if desired, for one of the two cyclohexane rings tobe replaced by 1.4-phenylene, which may also, if desired, be laterallydifluorinated or preferably monofluorinated.

The liquid-crystal mixtures preferably comprise one or more compoundscontaining a structural unit of the formula i in which n is 2.

The liquid-crystal mixtures used in the liquid-crystal switchingelements according to the invention preferably comprise

a component A consisting of compounds having 2 six-membered rings,

a component B consisting of compounds having 3 six-membered rings, and,if desired,

a component C consisting of compounds having 4 six-membered rings.

The liquid-crystal mixtures preferably essentially consist of componentsA, B and, if desired, C.

Particularly preferred liquid-crystal mixtures comprise one or more

dielectrically neutral compounds of the formula I

in which

R¹¹ is n-alkyl having from 1 to 5 carbon atoms,

R¹² is n-alkyl having from 1 to 5 carbon atoms, 1E-alkenyl, preferablyvinyl, or n-alkoxy having from 1 to 6 carbon atoms,

optionally dielectrically positive compounds selected from the groupconsisting of the formulae II and II′

in which

R²¹ is n-alkyl or 1E-alkenyl having from 3 to 7 or from 2 to 8,preferably from 5 to 7 or from 4 to 6 carbon atoms respectively,

Z² is a single bond or —CH₂CH₂—

and

X² is OCF₃, CF₃ or CH₂CH₂CF₃, preferably CF₃ or CH₂CH₂CF₃,

in which

R^(2′) is n-alkyl or 1E-alkenyl having from 3 to 7 or from 2 to 8,preferably having from 5 to 7 or from 4 to 6 carbon atoms respectively,

Z^(2′) is a single bond or —CH₂CH₂—,

X^(2′) is OCF₂H, OCF₃ or F, preferably F,

and

Y^(2′) and Z^(2′), independently of one another, are H or F,

and

compounds of the formula III

in which

R³¹ is n-alkyl or 1E-alkenyl having from 2 to 7, preferably from 2 to 5,carbon atoms,

Z³¹ and Z³² may each be a single bond of Z³¹ and Z³² and —CH₂CH₂— or—CF₂CF₂—, preferably —CH₂CH₂, but particularly preferably are both asingle bond,

X³ is OCF₂, OCF₃ or F,

Y³ and Z³, independently of one another, are H or F,

in the case of

X³=OCF₂ both Y³ and Z³ are preferably F,

in the case of

X³=F both Y³ and Z³ are preferably F,

in the case of

X³=OCF₃ one of Y³ and Z³ is preferably F, and the other is H,

optionally one or more compounds selected from the group consisting ofthe compounds of the formulae IV and V

in which

R⁴ is n-alkyl or 1E-alkenyl having from 2 to 5, preferably having from 2to 5 carbon atoms,

X⁴ is OCF₂H, OCF₃ or F, preferably F or OCF₃,

Y⁴ and Z⁴, independently of one another, are H or F,

in the case of

X=F and

both Y⁴ and Z⁴ are preferably F

in the case of

X=OCF₃ and particularly preferably in the case of

one of Y³ and Z³ is F, and the other is H.

in which

R⁵ is n-alkyl or 1E-alkenyl having from 2 to 5 carbon atoms,

Z⁵¹ is a single bond or —CH₂CH₂—,

X⁵ is F, OCF₃ or OCF₂H,

Y⁵ and Z⁵, independently of one another, are H or F,

preferably

X⁵, Y⁵ and Z⁵ are all F,

optionally one or more compounds of high clearing point selected fromthe group consisting of the compounds of the formulae VI to XI

in which R⁷¹ and R⁷², R⁸¹ and R⁸², R⁹¹ and R⁹², R¹⁰ and R¹¹ are each,independently of one another, as defined above for R¹¹ and R¹² in theformulae I,

L⁸¹ and L⁹¹ are H or F, and

X¹⁰, Y¹⁰ and Z¹⁰, and X¹¹, Y¹¹ and Z¹¹ are each, independently of oneanother, as defined above for X³, Y³, and Z³ in the formulae III.

The liquid-crystal mixtures in accordance with the present applicationpreferably comprise from 4 to 36 compounds, particularly preferably from6 to 25 compounds and very particularly preferably from 7 to 20compounds.

Particularly preferred liquid-crystal mixtures comprise one or morecompounds selected from the group consisting of the following compoundsfrom Table 3 and especially preferably in each case one or morecompounds of at least three, preferably of at least four, differentformulae of those listed in Table 3 below.

TABLE 3 Preferred compounds

The temperature range of the nematic phase preferably extends from −20°C. to 60° C., particularly preferably from −30° C. to 70° C. and veryparticularly from 40° C. to 80° C. The birefringence is preferably from0.040 to 0.070, particularly preferably from 0.050 to 0.065 and veryparticularly preferably from 0.054 to 0.063. The rotational viscosity ispreferably from 60 to 170 m Pa s, particularly preferably from 80 to 150m Pa s and very particularly preferably from 90 to 139 m Pa s. Thethreshold voltage (V₁₀) in the switching elements according to theinvention is preferably from 0.9 V to 2.7 V, particularly preferablyfrom 1.1 V to 2.5 V and very particularly preferably from 1.2 V to 2.0V. The sum response times for switching between V₁₀ and V₉₀ and back inthe switching elements according to the invention are preferably at most100 ms, particularly preferably at most 80 ms, very particularlypreferably 60 ms or less. For faster applications, the sum responsetimes are 50 ms or less, preferably 45 ms or less, particularlypreferably 40 ms or less, especially 40 ms or less and very particularlypreferably 30 ms or less.

Furthermore, the preferred parameters of the liquid-crystal mixtures canreadily be gathered by the person skilled in the art from the examplesshown below. In particular, the preferred ranges for the physicalproperties of the liquid-crystal mixtures and their combinations arethose which are covered by the values in the examples.

The liquid-crystal mixtures particularly preferably essentially consistof compounds selected from the group consisting of the compounds of theformulae I, II, II′ and III to XI.

The liquid-crystal media employed in the liquid-crystal switchingelements in accordance with the present invention preferably consist offrom 3 to 35 compounds, particularly preferably of from 4 to 25, veryparticularly preferably of from 5 to 20 and especially preferably offrom 6 to 15 compounds.

The preferred d/P range is from −0.25 to 0.25. For the lowest possibleaddressing voltages, a d/P in the range from −0.1 to 0.1, particularly0, is preferred. For optimum display of grey shades and in order tosuppress inverse contrast, d/P values having a figure of from 0.1 to0.25, particularly from 0.15 to 0.24, are preferred.

In the present application, the following apply, unless expressly statedotherwise:

the physical properties were determined as described in: Merck LiquidCrystals, Physical Properties of Liquid Crystals, Description of theMeasurement Methods, Ed. W. Becker, Status Nov. 1997,

all physical data are given for a temperature of 20° C.,

all temperatures are given in ° C. and all temperature differences indifferential degrees,

all concentration data are in % by weight,

Δn (Δn=n_(∥)−n_(⊥)) relates to 589.3 nm,

Δε (Δε=ε_(∥)−ε_(⊥)) relates to 1 kHz,

γ₁: rotational viscosity,

k_(il): elastic constants,

λ is 576 nm,

V₀: capacitive threshold or alternatively Freedericks threshold,

V₁₀: threshold voltage (for 10% relative contrast, Θ=0°),

V₅₀: mid-grey voltage (for 50% relative contrast, Θ=0°),

V₉₀: saturation voltage (for 90% relative contrast, Θ=0°),

τ_(delay): dead time from 0% to 10% change in the relative contrast,

τ_(rise): rise time from 10% to 90% change in the relative contrast,

τ_(on): switch-on time from 0% to 90% change in the relative contrast,

τ_(off): switch-off time from 90% to 10% change in the relativecontrast,

τ_(sum): sum response time=τ_(on)+τ_(off),

Φand Φ′: observation angle in the display plane,

Θ: observation angle from the display normal,

φ: twist angle of the liquid-crystal director between the twosubstrates,

φ: tilt angle of the liquid-crystal director,

φ₀: tilt angle of the liquid-crystal director at the substrate surfaceor at the alignment layer,

φ_(m): tilt angle of the liquid-crystal director in the centre of theliquid-crystal layer,

Ψ_(PP) (identical with Ψ_(PA)): angle between the transmission axes ofthe polarisers,

Ψ_(PD): angle between the transmission axis of the polariser and thefast axis of the birefringent layer,

Ψ_(PL) and Ψ_(AL): angle between the transmission axis of the polariseror of the analyser and the alignment direction of the liquid-crystalmaterial at the respective adjacent substrate,

the electro-optical properties and response times were determined withrectangular alternating voltage addressing with a frequency of 60 Hz,

the stated voltage values are root mean square (rms) values,

“essentially 0” means, unless stated otherwise, 0+/−1, preferably0+/−0.1 and particularly preferably 0+/−0.1,

“essentially” in connection with physical properties means, unlessstated otherwise, with a deviation of not greater than +/−10%,preferably +/−5% and particularly preferably +/−2% of the respectivevalue,

“essentially consisting of” means, unless stated otherwise, that theproportion of other constituents is not greater than 10%, preferably notgreater than 5% and particularly preferably not greater than 2%,

the numerical values given in the present application are, unless statedotherwise, accurate to +/− one unit in the final place given,

limits of the ranges indicated are, unless stated otherwise, inclusive,but preferably exclusive,

>= and <=, >/= and </=, and ≧ and ≦ in each case mean less than or equalto or greater than or equal to respectively, and

+/− means plus or minus.

The rotational viscosity of the nematic liquid-crystal mixture ZLI-4792(Merck KGaA) at 20° C. using the calibrated rotational viscometer was133 mPa·s.

The electro-optical properties were investigated in test cells fromMerck KGaA's production:

Layer thickness:

Glass: borosilicate glass with a thickness of 1.1 mm (Pilkington)

ITO: 100 ohm/square inch (i/square inch)

Alignment layer: AL-1054 from Japan Synthetic Rubber, Japan,

Tilt angle: from 1° to 2° (determined using liquid-crystal materialZLI-4792 from Merck KGaA, Germany,

Twist angle: 0° (glass plates subjected to antiparallel rubbing),

d/P: 0 (undoped).

The optical and electro-optical properties of the test cells weremeasured in commercial instruments from Autronic-Melchers, Karlsruhe,Germany (DMS 301 and DMS 703) and in addition in a home-made instrumentfrom Merck KGaA, in each case using white light. The home-madeinstrument uses a photomultiplier as detector and a filter for matchingthe addressing sensitivity of the detector to the sensitivity curve ofthe human eye.

In the home-made instrument from Merck KGaA, the λ/4 layer waspermanently mounted as a platelet in the ray path. In the case of themeasurements with the DMS 703, a λ/4 film of liquid-crystalline polymerfrom Merck Ltd, Great Britain, was used.

In the present application and in particular in the examples, theliquid-crystal compounds are denoted by abbreviations. The coding of thestructures is obvious and is carried out in accordance with Tables A andB. All groups C_(n)H_(2n+1), C_(m)H_(2m+1) C_(l)H_(2l+1) andC_(k)H_(2k+)1 are straight-chain alkyl chains having n, m, l and kcarbon atoms respectively. The coding in Table B is self-explanatory.Table A shows only the respective skeletons of the structures. Theindividual compounds are indicated below through specification of thedesignation of the core followed, separated by a dash, by thedesignation for the substituents R¹, R², L¹ and L²:

Code for R¹, R², L¹, L² R¹ R² L¹ L² nm C_(n)H_(2n+1) C_(m)H_(2m+1) H HnOm C_(n)H_(2n+1) OC_(m)H_(2m+1) H H nO.m OC_(n)H_(2n+1) C_(m)H_(2m+1) HH n C_(n)H_(2n+1) CN H H nN.F C_(n)H_(2n+1) CN F H nOF OC_(n)H_(2n+1) FH H nCl C_(n)H_(2n+1) Cl H H nCl.F C_(n)H_(2n+1) Cl F H nCl.F.FC_(n)H_(2n+1) Cl F F nF C_(n)H_(2n+1) F H H nF.F C_(n)H_(2n+1) F F HnF.F.F C_(n)H_(2n+1) F F F nmF C_(n)H_(2n+1) C_(m)H_(2m+1) F H nCF₃C_(n)H_(2n+1) CF₃ H H nOCF₃ C_(n)H_(2n+1) OCF₃ H H nOCF₃.F C_(n)H_(2n+1)OCF₃ F H nOCF₃.F.F C_(n)H_(2n+1) OCF₃ F F nOCF₂ C_(n)H_(2n+1) OCHF₂ H HnOCF₂.F C_(n)H_(2n+1) OCHF₂ F H nOCF₂.F.F C_(n)H_(2n+1) OCHF₂ F F nSC_(n)H_(2n+1) NCS H H nVsN C_(r)H_(2r+1)—CH═CH—C_(s)H_(2s)— CN H H nEsNC_(r)H_(2r+1)—O—C_(s)H_(2s)— CN H H nAm C_(n)H_(2n+1) COOC_(m)H_(2m+1) HH

TABLE A

TABLE B

The liquid-crystal mixtures of the present invention preferablycomprise:

four or more compounds selected from the group consisting of thecompounds from Tables A and B and/or

five or more compounds selected from the group consisting of thecompounds from Table B and/or

two or more compounds selected from the group consisting of thecompounds from Table A.

The effect of the present invention is illustrated below with referenceto figures and examples and compared with the prior art.

EXAMPLES

The following examples are intended to explain the present inventionwithout restricting it in any way. However, the descriptive embodimentsare preferred and confirm the variation range for the various parametersof the liquid-crystal switching elements and those of the liquid-crystalmixtures and their composition. The person skilled in the art will beable to deduce preferred ranges for these conditions and propertiesdirectly from the examples.

Example 1

A liquid-crystal switching element having an antiparallel edge alignmentand a polyimide alignment layer, a twist angle of 0° and a surface tiltangle of 1.4° was produced. The switching element contained a λ/4 layerand crossed polarisers, which adopted an angle of 45° to the rubbingdirection of the substrates. The construction of the liquid-crystalswitching element corresponds to the structure shown in FIG. 1. Theoptical retardation of the liquid-crystal layer was 0.277 μm. Thecomposition of the liquid-crystal mixture used is indicated in thefollowing table, together with the properties of the mixture as such,and the characteristic voltages in the switching element according tothe invention.

Composition Conc./% Properties CCH-301 5.0 Transition T (S, N) < −30.0°C. CH-33 3.0 Clearing point T (N, I) = +68.0° C. CH-35 3.0 Δn (589 nm,20° C.) = +0.0602 CCP-2F.F.F 6.0 Δε (1 kHz, 20° C.) = +10.3 CCZU-2-F 6.0γ₁ (20° C.) = 161 m Pa s CCZU-3-F 16.0 d · Δn = 0.277 μm CCZU-5-F 6.0Twist = 0° CDU-2-F 10.0 V₀ (20° C.) = 0.99 V CDU-3-F 12.0 V₁₀ (20° C.) =1.29 V CDU-5-F 8.0 V₅₀ (20° C.) = 1.76 V CCH-3CF3 9.0 V₉₀ (20° C.) =3.15 V CCH-5CF3 12.0 CCPC-34 4.0 Σ 100.0

The liquid-crystal switching element was firstly investigated withrespect to its transmission on variation of the analyser angle. Theresult is shown in FIG. 3. The optical retardation was 277 nm.

It can be seen that minimal transmission occurs in the voltage-freestate with parallel polarisers, i.e. in each case at angles Ψ_(PP) of0°, 180° and 360°, and that this minimal transmission drops virtually to0%. These polarisation settings, which are identical with one another,correspond to the normally black mode. By contrast, with crossedpolarisers, i.e. at angles Ψ_(PP) of 90° and 270°, which correspond tothe normally white mode, maximum transmission occurs.

The electro-optical characteristic line was then recorded at variousobservation angles both with the home-made instrument and with theinstrument from Autronic-Melchers. The results obtained with thehome-made instrument for two cells in normally black mode at twoobservation angles Θ (Θ=0° and Θ=30°) in the quadrant having the bestcontrast (Φ=45°) are shown in FIG. 4 by way of example. The definitionof the observation angles Θ and Φ is shown in FIG. 2.

FIG. 2 shows the definition of the observation angles in the plane ofthe display (Φ and (Φ′) and perpendicular to the normal (Θ).

FIG. 4 shows the resultant transmission voltage characteristic lines fortwo switching elements. The results for the different cells were soreadily reproducible that they are in each case reproduced in a singlecurve. Two curves are shown. The first curve shows the results for thetwo different cells for Θ=0°. The second curve applies to Θ=30° andΦ=−45°. It clearly shows the flatter rise in the characteristic line ata greater viewing angle Θ.

The maximum transmission in the fully switched state is about 45%. It isessentially determined by the transmission of the polarisers. At highaddressing voltages of from about 6 to 7 V, very high transmission isachieved. The minimum transmission is predominantly dependent on thedegree of polarisation of the polarisers used.

The spectral distribution of the transmission for the switching elementaddressed with various voltages was subsequently determined. The resultsare shown in FIG. 7. Here, the wavelength dependencies of thetransmission of the liquid-crystal switching element according to theinvention are shown as continuous curves compared with those of a TNdisplay having a d·Δn=0.5 μm from Comparative Example 1 (dashed curves).The three sets of curves correspond to the addressing voltages for 10,50 and 90% relative contrast. It is striking that the spectraldistribution in both switching elements is virtually identical, and thatthe spectrum is virtually colourless. At most a slight drop in theintegral transmission can be observed in the element according to theinvention compared with the TN switching element.

The transmission of the addressed element in the hemisphere above theelement was then measured using the instrument from Autronic-Melchers,as shown in FIG. 8b). FIG. 8b) shows the results of the liquid-crystalswitching element according to the invention from the present Example 1and FIG. 8a) shows those of the conventional TN switching element fromComparative Example 1.

In FIG. 8, the depiction in polar coordinates has been selected (for thedefinition, see FIG. 2). The transmission is determined for each pointin the hemisphere above the liquid-crystal switching element with afixed addressing voltage which results in a minimum transmission of 10%.Points of equal transmission are denoted by the same grey shade. Theisotransmission lines are staggered at separations of 10% absolute ineach case. The darkest region corresponds to a transmission of from 0%to 10% inclusive, the next grey region from more than 10% to 20%inclusive, the pale grey region from more than 20% to 30% inclusive, andso on, the lower limit always being exclusive and the upper limitinclusive. The other regions having a transmission of greater than 30%are not shaded in grey.

In direct comparison of FIGS. 8b) and 8 a), the significantly lowerviewing-angle dependence of the transmission of the switching elementaccording to the invention in FIG. 8b) is clearly evident.

Finally, isocontrast measurements were carried out on liquid cells inaccordance with the present invention and on comparative cells using theinstrument from Autronic-Melchers. In these measurements, the twoaddressing voltages used were the threshold voltage (V₁₀) and thesaturation voltage (V₉₀) of the respective cell. The results are shownin FIG. 9.

The two addressing voltages were 1.13 V and 2.64 V for the cell of thepresent example. The result is shown in FIG. 9a). The individual curvesstand from the inside outward successively for contrast ratios of 7, 5,3, 2 and 1. The maximum contrast ratio here was 9.6, and the minimumcontrast ratio 0.58. The viewing-angle dependence of the contrast ratio(CR) over the entire viewing-angle range is thus very low. Only moderateinverse contrast occurs, with CR_(min)=0.58, with inverse contrast beingdenoted as contrast ratios of less than 1.

FIG. 9c) shows for direct comparison the results for the TN switchingelement of Comparative Example 1. The individual curves stand from theinside outward successively for contrast ratios of 10, 7, 5, 3, 2 and 1.Significant inverse contrast occurs here.

Furthermore, response times for various switching voltages weredetermined. Illustrative results are listed in Table 4. In particular incomparison with the results for the TN switching element of ComparativeExample 1, the surprisingly short response times of the switchingelements according to the invention are notable. The response times weredetermined from three different addressing conditions. In the first twoseries, the response times were determined from a change from a voltageof 0 volts to a fixed value and back. In the first series, the voltageof the switched-on state was 9.9 volts and in the second series it was5.0 volts. In the third series, switching was carried out from V₁₀ toV₉₀ and back. This corresponds to the switching of a display between twogrey shades. The results are shown in the following table (Table 4).

TABLE 4 Response times Example V_(off)/ V_(on)/ τ_(delay)/ τ_(rise)/τ_(on)/ τ_(off)/ τ_(sum)/ No. No. V V ms ms ms ms ms 1 CE 1 0 9.9 2.600.78 3.39 52.3 55.7 2 1 0 9.9 1.43 0.78 2.23 25.2 27.4 3 CE 1 0 5.0 9.652.3 56.5 4 1 0 5.0 9.6 24.8 28.1 5 CE 1 1.11 1.73 3.39 34.4 37.8 83.6121.4 6 1 1.26 3.07 0.65 8.98 9.64 32.8 42.4

Comparative Example 1

A liquid-crystal switching element was produced and investigatedanalogously to Example 1, but now a TN switching element having anoptical retardation of 0.50 μm, without a further birefringent layer,with crossed polarisers, which were also crossed to the rubbingdirections.

The composition of the liquid-crystal mixture used is shown in thefollowing table, as are the properties of the mixture and thecharacteristic voltages of the TN element.

Composition Conc./% Properties BCH-2F.F 9.0 Clearing point T (N, I) =+69.5° C. BCH-3F.F 9.0 Δn (589 nm, 20° C.) = +0.1039 BCH-3F.F.F 5.0 Δε(1 kHz, 20° C.) = +10.2 BCH-5F.F.F 7.0 γ₁ (20° C.) = 156 m Pa s CGU-2-F10.0 d · Δn = 0.50 μm CGU-3-F 9.0 Twist = 90° CCP-3F.F.F 10.0 V₀ (20°C.) = 0.94 V CCP-5F.F.F 6.0 V₁₀ (20° C.) = 1.08 V CCZU-2-F 4.0 V₅₀ (20°C.) = 1.35 V CCZU-3-F 13.0 V₉₀ (20° C.) = 1.72 V CCG-V-F 15.0 BCH-32 3.0Σ 100.0

The electro-optical characteristic line of the TN switching element isshown in FIG. 5. Cells were investigated at Θ=0°. The results wereidentical. Compared with FIG. 4, FIG. 5 shows that the characteristiclines of the TN switching element having d·Δn of 0.5 μm (correspondingto the 1st Gooch and Tarry minimum) of this Comparative Example 1 aresignificantly steeper and thus less favourable for the display of greyshades than those of the liquid-crystal switching element according tothe invention from Example 1.

It should be noted here that both in normally white mode and in normallyblack mode, the reduction in the steepness of the characteristic line ofthe switching elements according to the invention is most pronounced athigh voltages, in contrast to the prior art. Since the human eye reactsmore sensitively to changes in transmission in the region of lowtransmission (i.e. lower brightness) than in the region of hightransmission (i.e. greater brightness), the effect is more favourable innormally white mode than in normally black mode since it occurs in theregion of lower transmission in normally white mode.

The spectral distribution of the transmission is compared in FIG. 7directly with that of the element from Example 1 and has already beendiscussed in Example 1.

FIG. 8a) shows the isotransmission results for this Comparative Example1, which were obtained under the same conditions as the results forExample 1. The results have already been discussed in Example 1.

FIG. 9c) shows the isocontrast results obtained under the sameconditions as in Example 1. The two addressing voltages were 1.07 V and1.71 V, corresponding to V₁₀ and V₉₀ respectively. The individual curvesstand from the inside outward successively for contrast ratios of 10, 7,5, 3, 2 and 1. The maximum contrast ratio was 15, and the minimumcontrast ratio was 0.43. The viewing-angle dependence of the contrast isthus obviously much more pronounced than in the case of the switchingelements from Examples 1 and 2. In addition, significant inversecontrast occurs. The apparently greater maximum contrast ratio comparedwith Examples 1 and 2 is presumably attributable to the measurementconditions. In separate measurements of the transmission with verticalobservation and with addressing with sufficiently high voltages, thesame contrast was determined for all three types of switching element.

The response times are also shown in Table 4. As is clearly evident fromTable 4, the sum response time of the switching element according to theinvention is virtually halved under each of the three addressingconditions compared with that of the conventional TN switching element.This is all the more surprising since both switching elements have thesame layer thickness (in each case 4.8 μm). Even the rotationalviscosities cannot explain the observed change in the response times.The rotational viscosity of the liquid-crystal mixture from Example 1 isvirtually exactly as large as that of the liquid-crystal mixture ofComparative Example 1. It is even about 3% greater, from which acorresponding small increase in the response times for the switchingelement according to the invention would rather have been expected.

Example 2

A switching element like that of Example 1 was produced, with theconstruction apart from one exception. No λ/4 layer was used.

The switching element had virtually the same electro-opticalcharacteristic lines at an observation angle of 0° as that of Example 1,both in the home-made instrument and in the instrument fromAutronic-Melchers. The maximum contrast was also virtually identicalwith that of Example 1.

The viewing-angle dependency of the contrast was excellent on visualassessment. This was confirmed by measurement of the isocontrast curvesunder the same conditions as in Example 1. As in Example 1, the twoaddressing voltages were 1.13 V and 2.64 V. The result is shown in FIG.9b). The individual curves stand from the inside outward successivelyfor the same contrast ratios as in FIG. 9a), with merely the last curvebeing omitted, i.e. for 7, 5, 3 and 2. The maximum contrast ratio herewas 10.0, and the minimum 1.08. Thus, absolutely no inverse contrast atall occurred under these conditions.

The direct comparison between the values for the switching elements ofExamples 1 and 2 gives the following. Based on the observation angle Θ,Example 2 clearly has the broader, i.e. better, viewing-angle range. Theelement of Example 2 is also slightly superior to that of Example 1 withrespect to integral observation. By contrast, the viewing-angle range ofthe element from Example 1 is therefore significantly better withrespect to the observation angle Φ). This is particularly evident in theregion of the quadrant having the lowest contrast. The viewing-anglerange of the switching element from Example 1 is significantly morecentrosymmetrical.

Example 3

A switching element was produced as in Example 1 with a λ/4 plate.However, the liquid-crystal material used here was ZLI-4792, acommercial product from Merck KGaA. This material has a birefringence of0.0969. The layer thickness of the liquid-crystal layer was 5.1 μm. Theelectro-optical characteristic line for a normally black switchingelement (having parallel polarisers) was determined at an observationangle of Φ=45° and Θ=10°, as described in Example 1. The result is shownin FIG. 6.

In this FIG. 6, the characteristic line of a TN switching element havingd·Δn of 0.50 μm and of a switching element according to the invention,both with virtually the same capacitive threshold, also known as theFreedericks threshold, are shown in comparison. The curves were obtainedat observation angles of Θ=100, Φ=45°. In direct comparison with thisliquid-crystal switching element from the prior art, it is striking thatthe switching element according to the invention has both significantlylower steepness than the comparable TN switching element and alsoexhibits absolutely no signs of inverse contrast, with virtuallyunchanged maximum transmission. The switching element according to theinvention is consequently significantly more suitable for the display ofgrey shades and in particular of colour shades.

Comparative Example 2

A switching element was produced analogously to Example 3 usingZLI-4792, but this time a TN switching element at the first transmissionminimum (optical retardation 0.50 μm) was produced as in ComparativeExample 1. As in Example 3, the electro-optical characteristic line wasdetermined at an observation angle of Φ=45° and Θ=10°. The result isshown in FIG. 6 for comparison with that from Example 3.

The occurrence of inverse contrast, i.e. the reversal of the slope ofthe electro-optical characteristic line with increasing voltage, isclearly evident in the curve for the TN switching element from a voltageof about 2.4 volts. By contrast, the characteristic line of theswitching element according to the invention is significantly flatter,i.e. has a smaller slope (also known as steepness), which is moresuitable for the display of grey shades. In addition, absolutely noinverse contrast at all occurs at this viewing angle in the switchingelement according to the invention.

FIG. 6 shows the characteristic line of the liquid-crystal switchingelement according to the invention with that of the TN switching elementfrom Comparative Example 1. Both switching elements have virtually thesame capacitive threshold, also known as the Freedericks threshold. Thecurves were obtained at observation angles of Θ=10° and Φ=−45°. Indirect comparison with this liquid-crystal switching element from theprior art, it is striking that the switching element according to theinvention has both significantly lower steepness than the comparable TNswitching element and also exhibits absolutely no signs of inversecontrast, with virtually unchanged maximum transmission. The switchingelement according to the invention is consequently significantly moresuitable for the display of grey shades and in particular of colourshades.

Further examples (No. 4 to 63) of switching elements and liquid-crystalmixtures according to the invention are given in abbreviated form below.For simplification, only the characteristic voltages V₁₀, V₅₀ and V₉₀,which were determined from the electro-optical characteristic lines fornormally white switching elements according to Example 1, as describedtherein, are shown for the switching elements.

Example 4

Composition Conc./% Properties CC-5-V 14.0 Transition T (S, N) < −40.0°C. CCH-303 3.0 Clearing point T (N, I) = +76.0° C. CCH-501 5.0 Δn (559nm, 20° C.) = +0.0597 CCP-2F.F.F 10.0 Δε (1 kHz, 20° C.) = +5.5CCP-3F.F.F 12.0 γ₁ (20° C.) [m Pa s] CCP-5F.F.F 4.0 V₁₀ (20° C.) = 1.80V CCZU-2-F 5.0 V₅₀ (20° C.) = 2.48 V CCZU-3-F 16.0 V₉₀ (20° C.) = 4.44 VCCZU-5-F 5.0 CCH-301 18.0 CH-33 2.0 CH-35 3.0 CH-45 3.0 Σ 100.0

Example 5

Composition Conc./% Properties CC-5-V 6.0 Transition T (S, N) < −40.0°C. CCH-34 5.0 Clearing point T (N, I) = +75.0° C. CCH-501 6.0 Δn (589nm, 20° C.) = +0.0604 CCP-2F.F.F 12.0 Δε (1 kHz, 20° C.) = +6.4CCP-3F.F.F 12.0 V₁₀ (20° C.) = 1.60 V CCP-5F.F.F 5.0 V₅₀ (20° C.) = 2.23V CCZU-2-F 6.0 V₉₀ (20° C.) = 3.95 V CCZU-3-F 20.0 CCZU-5-F 5.0 CCH-30118.0 CH-35 2.0 CH-45 3.0 Σ 100.0

Example 6

Composition Conc./% Properties CCH-3CF3 8.0 Transition T (S, N) < −40.0°C. CCH-5CF3 12.0 Clearing point T (N, I) = +72.0° C. CC-5-V 5.0 Δn (589nm, 20° C.) = +0.0578 CCH-303 5.0 Δε (1 kHz, 20° C.) = +6.5 CCH-501 12.9γ₁ (20° C.) = 129 m Pa s CCP-2F.F.F 12.0 V₁₀ (20° C.) = 1.72 CCP-3F.F.F6.0 V₅₀ (20° C.) = 2.34 V CCZU-2-F. 6.0 V₉₀ (20° C.) = 4.13 V CCZU-3-F19.0 CCZU-5-F 6.0 CH-33 3.0 CH-35 3.0 CCPC-34 3.0 Σ 100.0

Example 7

Composition Conc./% Properties CC-5-(S)3 10.0 Transition T (S, N) <−40.0° C. CCH-301 6.0 Clearing point T (N, I) = +70.5° C. CCH-303 5.0 Δn(589 nm, 20° C.) = +0.0568 CCH-501 14.0 Δε (1 kHz, 20° C.) = +5.8CCP-2F.F.F 12.0 γ₁ (20° C.) = 142 m Pa s CCP-3F.F.F 12.0 V₁₀ (20° C.) =1.64 V CCZU-2-F 6.0 V₅₀ (20° C.) = 2.23 V CCZU-3-F 22.0 V₉₀ (20° C.) =3.98 V CCZU-5-F 6.0 CH-33 3.0 CCPC-34 4.0 Σ 100.0

Example 8

Composition Conc./% Properties CC-5-V 14.0 Clearing point T (N, I) =+76.0° C. CCH-301 18.0 Δn (589 nm, 20° C.) = +0.0608 CCH-303 3.0 Δε (1kHz, 20° C.) = +5.5 CCH-501 5.0 V₁₀ (20° C.) = 1.77 V CCP-2F.F.F 10.0V₉₀ (20° C.) = 4.28 V CCP-3F.F.F 12.0 CCP-5F.F.F 4.0 CCZU-2-F 5.0CCZU-3-F 16.0 CCZU-5-F 5.0 CH-33 2.0 CH-35 3.0 CH-45 3.0 Σ 100.0

Example 9

Composition Conc./% Properties CC-5-V 6.0 Clearing point T (N, I) =+75.5° C. CCH-301 18.0 Δn (559 nm, 20° C.) = +0.0596 CCH-34 5.0 Δε (1kHz, 20° C.) = +6.4 CCH-501 6.0 V₁₀ (20° C.) = 1.63 V CCP-2F.F.F 12.0V₉₀ (20° C.) = 3.91 V CCP-3F.F.F 12.0 CCP-5F.F.F 5.0 CCZU-2-F 6.0CCZU-3-F 20.0 CCZU-5-F 5.0 CH-35 2.0 CH-45 3.0 Σ 100.0

Example 10

Composition Conc./% Properties CCH-501 12.0 Transition T (S, N) < −40.0°C. CH-33 4.0 Clearing point T (N, I) = +81.0° C. CH-35 4.0 Δn (589 nm,20° C.) = +0.0610 CH-43 4.0 Δε (1 kHz, 20° C.) = +8.9 CCP-2F.F.F 9.0 γ₁(20° C.) = 154 m Pa s CCZU-2-F 6.0 V₁₀ (20° C.) = 1.49 V CCZU-3-F 16.0V₉₀ (20° C.) = 3.55 V CCZU-5-F 6.0 CDU-2-F 9.0 CDU-3-F 11.0 CCH-3CF3 7.0CCH-5CF3 8.0 CCPC-34 4.0 Σ 100.0

Example 11

Composition Conc./% Properties ECCH-5CF3 20.0 Clearing point T (N, I) =+74.0° C. CC-5-V 5.0 Δn (589 nm, 20° C.) = +0.0585 CCH-303 5.0 Δε (1kHz, 20° C.) = +6.5 CCH-501 12.0 γ₁ (20° C.) = 141 m Pa s CCP-2F.F.F12.0 V₁₀ (20° C.) = 1.79 V CCP-3F.F.F 6.0 V₉₀ (20° C.) = 4.27 V CCZU-2-F6.0 CCZU-3-F 19.0 CCZU-5-F 6.0 CH-33 3.0 CH-35 3.0 CCPC-34 3.0 Σ 100.0

Example 12

Composition Conc./% Properties CC-5-V 10.0 Transition T (S, N) < −40.0°C. CCP-20CF3 6.0 Clearing point T (N, I) = +77.0° C. CCP-40CF3 4.0 Δn(589 nm, 20° C.) = +0.0608 CCP-2F.F.F 11.0 Δε (1 kHz, 20° C.) = +5.4CCP-3F.F.F 11.0 V₁₀ (20° C.) = 1.91 V CCP-5F.F.F 6.0 V₉₀ (20° C.) = 4.66V CCP-20CF3.F 9.0 CCZU-2-F 5.0 CZU-3-F 10.0 CCPC-34 3.0 CC-5-(T)5 15.0CC-5-(T1)5 10.0 Σ 100.0

Example 13

Composition Conc./% Properties CCH-501 12.0 Transition T (S, N) < −40.0°C. CH-33 3.0 Clearing point T (N, I) = +81.5° C. CH-35 3.0 Δn (589 nm,20° C.) = +0.0604 CH-43 3.0 Δε (1 kHz, 20° C.) = +8.4 CH-45 3.0 γ₁ (20°C.) = 160 m Pa s CCP-2F.F.F 9.0 V₀ (20° C.) = 1.22 V CCZU-2-F 6.0 V₁₀(20° C.) = 1.51 V CZU-3-F 15.0 V₅₀ (20° C.) = 2.03 V CZU-5-F 6.0 V₉₀(20° C.) = 3.59 V CDU-2-F 9.0 CDU-3-F 9.0 CDU-5-F 3.0 CCH-3CF3 7.0CCH-5CF3 8.0 CCPC-34 4.0 Σ 100.0

Example 14

Composition Conc./% Properties CCH-301 17.0 Transition T (S, N) < −40.0°C. CCH-501 14.0 Clearing point T (N, I) = +81.0° C. CCH-34 4.0 Δn (589nm, 20° C.) = +0.0598 CH-33 3.0 Δε (1 kHz, 20° C.) = +7.1 CH-35 3.0 V₁₀(20° C.) = 1.65 V CH-43 3.0 V₉₀ (20° C.) = 3.96 V CCPC-34 4.0 CCZU-2-F4.0 CCZU-3-F 17.0 CCZU-5-F 5.0 CDU-2-F 9.0 CDU-3-F 9.0 CDU-5-F 8.0 Σ100.0

Example 15

Composition Conc./% Properties CCH-301 14.0 Transition T (S, N) < −40.0°C. CCH-34 4.0 Clearing point T (N, I) = +78.0° C. CC-5-V 5.0 Δn (559 nm,20° C.) = +0.0601 CCP-2F.F.F 10.0 Δε (1 kHz, 20° C.) = +6.6 CCP-3F.F.F12.0 V₁₀ (20° C.) = 1.72 V CCP-5F.F.F 6.0 V₉₀ (20° C.) = 4.17 V CCZU-2-F5.0 CCZU-3-F 16.0 CCZU-5-F 5.0 CCP-20CF3.F 2.0 CCH-3CF3 10.0 CH-33 3.0CH-35 3.0 CH-43 3.0 CH-45 2.0 Σ 100.0

Example 16

Composition Conc./% Properties CCH-301 16.0 Transition T (S, N) < −40.0°C. CCH-501 16.0 Clearing point T (N, I) = +95.5° C. CCH-35 3.0 Δn (589nm, 20° C.) = +0.0608 CCH-5CF3 5.0 Δε (1 kHz, 20° C.) = +4.5 CCP-2F.F.F10.0 V₁₀ (20° C.) = 2.26 V CCP-3F.F.F 8.0 V₉₀ (20° C.) = 5.41 V CCZU-2-F4.0 CCZU-3-F 13.0 CCZU-5-F 4.0 CCPC-33 3.0 CCPC-34 4.0 CCPC-35 4.0CCOC-3-3 3.0 CCOC-4-3 5.0 CCOC-3-5 2.0 Σ 100.0

Example 17

Composition Conc./% Properties CCH-301 14.0 Clearing point T (N, I) =+71.0° C. CCH-303 18.0 Δn (589 nm, 20° C.) = +0.0593 CCH-501 4.0 Δε (1kHz, 20° C.) = +4.0 CCH-34 6.0 CCH-35 6.0 CCP-20CF3 5.0 CCP-40CF3 5.0CCP-50CF3 7.0 CCP-2F.F.F 12.0 CCP-3F.F.F 15.0 CCP-5F.F.F 8.0 Σ 100.0

Example 18

Composition Conc./% Properties CC-5-V 14.0 Transition T (S, N) < −40.0°C. CCH-303 3.0 Clearing point T (N, I) = +76.0° C. CCH-501 5.0 Δn (589nm, 20° C.) = +0.0597 CCP-2F.F.F 10.0 Δε (1 kHz, 20° C.) = +5.5CCP-3F.F.F 12.0 V₁₀ (20° C.) = 1.80 V CCP-5F.F.F 4.0 V₉₀ (20° C.) = 4.44V CCZU-2-F 5.0 CCZU-3-F 16.0 CCZU-5-F 5.0 CCH-301 18.0 CH-33 2.0 CH-353.0 CH-45 3.0 Σ 100.0

Example 19

Composition Conc./% Properties CC-5-V 6.0 Transition T (S, N) < −40.0°C. CCH-34 5.0 Clearing point T (N, I) = +75.0° C. CCH-501 6.0 Δn (589nm, 20° C.) = +0.0604 CCP-2F.F.F 12.0 Δε (1 kHz, 20° C.) = +6.4CCP-3F.F.F 12.0 V₁₀ (20° C.) = 1.60 V CCP-5F.F.F 5.0 V₉₀ (20° C.) = 3.94V CCZU-2-F 6.0 CCZU-3-F 20.0 CCZU-5-F 5.0 CCH-301 18.0 CH-35 2.0 CH-453.0 Σ 100.0

Example 20

Composition Conc./% Properties CC-5-V 4.0 Clearing point T (N, I) =+70.0° C. CCH-34 5.0 Δn (589 nm, 20° C.) = +0.0601 CCH-501 7.0 Δε (1kHz, 20° C.) = +6.6 CCP-2F.F.F 11.0 V₁₀ (20° C.) = 1.57 V CCP-3F.F.F12.0 V₉₀ (20° C.) = 3.89 V CCP-5F.F.F 5.0 CCZU-2-F 6.0 CCZU-3-F 20.0CCZU-5-F 6.0 CCH-301 20.0 CH-35 2.0 CCP-20CF2.F.F 2.0 Σ 100.0

Example 21

Composition Conc./% Properties CCH-301 23.0 Clearing point T (N, I) =+70.0° C. CCH-303 3.0 Δn (589 nm, 20° C.) = +0.0610 CCH-501 4.0 Δε (1kHz, 20° C.) = +4.1 CCP-30CF3 3.0 V₁₀ (20° C.) = 2.10 V CCP-40CF3 3.0V₉₀ (20° C.) = 5.05 V CCP-50CF3 3.0 CCP-2F.F.F 5.0 CCP-3F.F.F 10.0CCP-5F.F.F 8.0 CC-5-V 16.0 CCP-30CF3.F 6.0 CCP-50CF3.F 8.0 CCP-30CF2.F.F4.0 CCP-50CF2.F.F 4.0 Σ 100.0

Example 22

Composition Conc./% Properties CCH-301 23.0 Clearing point T (N, I) =+70.0° C. CCH-303 3.0 Δn (589 nm, 20° C.) = +0.0610 CCH-501 4.0 Δε (1kHz, 20° C.) = +4.1 CCP-30CF3 3.0 V₁₀ (20° C.) = 2.10 V CCP-40CF3 3.0V₉₀ (20° C.) = 5.05 V CCP-50CF3 3.0 CCP-2F.F.F 5.0 CCP-3F.F.F 10.0CCP-5F.F.F 8.0 CC-5-V 16.0 CCP-30CF3.F 6.0 CCP-50CF3.F 8.0 CCP-30CF2.F.F4.0 CCP-50CF2.F.F 4.0 Σ 100.0

Example 23

Composition Conc./% Properties CC-5-V 16.0 Transition T (S, N) < −30.0°C. CCH-301 16.0 Clearing point T (N, I) = +86.0° C. CCH-303 3.0 Δn (589nm, 20° C.) = +0.0606 CCH-501 5.0 Δε (1 kHz, 20° C.) = +4.0 CCP-2F.F.F7.0 γ₁ (20° C.) = 123 m Pa s CCP-3F.F.F 5.0 V₁₀ (20° C.) = 2.18 VCCZU-2-F 4.0 V₉₀ (20° C.) = 5.30 V CCZU-3-F 13.0 CCZU-5-F 4.0 CH-33 2.0CH-35 3.0 CH-43 2.0 CH-45 3.0 CCPC-34 3.0 CCPC-35 2.0 CCP-50CF2.F.F 7.0PCH-7F 5.0 Σ 100.0

Example 24

Composition Conc./% Properties CCH-301 20.0 Transition T (S, N) < −40.0°C. CCH-501 16.0 Clearing point T (N, I) = +95.0° C. CC-5-V 11.5 Δn (589nm, 20° C.) = +0.0604 CDU-2-F 6.0 Δε (1 kHz, 20° C.) = +4.0 CDU-3-F 6.0γ₁ (20° C.) = 127 m Pa s CDU-5-F 3.0 V₁₀ (20° C.) = 2.31 V CCZU-2-F 3.0V₉₀ (20° C.) = 5.55 V CCZU-3-F 11.0 CCZU-5-F 3.0 CH-33 3.0 CH-35 2.0CH-43 2.5 CCPC-33 5.0 CCPC-34 4.0 CCPC-35 4.0 Σ 100.0

Example 25

Composition Conc./% Properties CCH-301 18.0 Clearing point T (N, I) =+80.0° C. CCH-501 8.0 Δn (589 nm, 20° C.) = +0.0602 CCH-34 5.0 Δε (1kHz, 20° C.) = +7.9 CH-33 3.0 CH-35 3.0 CH-45 3.0 CCPC-34 3.0 CCZU-2-F5.0 CCZU-3-F 17.0 CCZU-5-F 5.0 CDU-2-F 11.0 CDU-3-F 12.0 CDU-5-F 7.0 Σ100.0

Example 26

Composition Conc./% Properties CCH-301 12.0 Transition T (S, N) < −30.0°C. CCH-501 8.0 Clearing point T (N, I) = +80.0° C. CC-5-V 8.0 Δn (589nm, 20° C.) = +0.0606 CCP-2F.F.F 10.0 Δε (1 kHz, 20° C.) = +6.3CCP-3F.F.F 12.0 CCP-5F.F.F 5.0 CCZU-2-F 5.0 CCZU-3-F 17.0 CCZU-5-F 5.0CH-33 3.0 CH-35 3.0 CH-43 3.0 CCH-3CF3 7.0 CCPC-33 2.0 Σ 100.0

Example 27

Composition Conc./% Properties CCH-301 14.0 Transition T (S, N) < −30.0°C. CCH-501 11.0 Clearing point T (N, I) = +80.0° C. CCP-2F.F.F 10.0 Δn(589 nm, 20° C.) = +0.0607 CCP-3F.F.F 13.0 Δε (1 kHz, 20° C.) = +6.5CCP-5F.F.F 5.0 CCZU-2-F 5.0 CCZU-3-F 17.0 CCZU-5-F 5.0 CH-33 3.0 CH-353.0 CH-43 3.0 CCPC-33 3.0 CCH-3CF3 8.0 Σ 100.0

Example 28

Composition Conc./% Properties CC-5-V 4.0 Clearing point T (N, I) =+70.0° C. CCH-34 5.0 Δn (589 nm, 20° C.) = +0.0601 CCH-301 20.0 Δε (1kHz, 20° C.) = +6.6 CCH-501 7.0 CH-35 2.0 CCP-2F.F.F 11.0 CCP-3F.F.F12.0 CCP-5F.F.F 5.0 CCZU-2-F 6.0 CCZU-3-F 20.0 CCZU-5-F 6.0CCP-20CF2.F.F 2.0 Σ 100.0

Example 29

Composition Conc./% Properties CCH-301 17.0 Transition T (S, N) < −30.0°C. CCH-501 6.0 Clearing point T (N, I) = +80.0° C. CC-5-V 14.0 Δn (589nm, 20° C.) = +0.0605 CCP-2F.F.F 10.0 Δε (1 kHz, 20° C.) = +5.7CCP-3F.F.F 10.0 γ₁ (20° C.) = 104 m Pa s CCP-5F.F.F 5.0 V₀ (20° C.) =1.50 V CCZU-2-F 5.0 CCZU-3-F 18.0 CCZU-5-F 6.0 CH-33 3.0 CH-35 3.0 CH-433.0 Σ 100.0

Example 30

Composition Conc./% Properties CCH-301 18.0 Clearing point T (N, I) =+81.0° C. CCH-501 5.0 Δn (589 nm, 20° C.) = +0.0604 CC-5-V 14.0 Δε (1kHz, 20° C.) = +5.5 CCP-2F.F.F 9.0 CCP-3F.F.F 13.0 CCP-5F.F.F 6.0CCZU-2-F 4.0 CCZU-3-F 16.0 CCZU-5-F 5.0 CH-33 2.0 CH-35 3.0 CH-43 2.0CH-45 3.0 Σ 100.0

Example 31

Composition Conc./% Properties CC-5-V 16.0 Transition T (S, N) < −30.0°C. CCH-301 16.0 Clearing point T (N, I) = +86.0° C. CCH-303 3.0 Δn (589nm, 20° C.) = +0.0606 CCH-501 5.0 Δε (1 kHz, 20° C.) = +4.0 CCP-2F.F.F7.0 V₁₀ (20° C.) = 2.18 V CCP-3F.F.F 5.0 V₉₀ (20° C.) = 5.30 V CCZU-2-F4.0 CCZU-3-F 13.0 CCZU-5-F 4.0 CH-33 2.0 CH-35 3.0 CH-43 2.0 CH-45 3.0CCPC-34 3.0 CCPC-35 2.0 CCP-50CF2.F.F 7.0 PCH-7F 5.0 Σ 100.0

Example 32

Composition Conc./% Properties CCH-301 20.0 Transition T (S, N) < −40.0°C. CCH-501 16.0 Clearing point T (N, I) = +95.0° C. CC-5-V 11.5 Δn (589nm, 20° C.) = +0.0604 CDU-2-F 6.0 Δε (1 kHz, 20° C.) = +4.0 CDU-3-F 6.0γ₁ (20° C.) = 127 m Pa s CDU-5-F 3.0 V₁₀ (20° C.) = 2.31 V CCZU-2-F 3.0V₉₀ (20° C.) = 5.53 V CCZU-3-F 11.0 CCZU-5-F 3.0 CH-33 3.0 CH-35 2.0CH-43 2.5 CCPC-33 5.0 CCPC-34 4.0 CCPC-35 4.0 Σ 100.0

Example 33

Composition Conc./% Properties CCH-301 18.0 Clearing point T (N, I) =+80.0° C. CCH-501 8.0 Δn (589 nm, 20° C.) = +0.0602 CCH-34 5.0 Δε (1kHz, 20° C.) = +7.9 CH-33 3.0 CH-34 3.0 CH-35 3.0 CCPC-34 3.0 CCZU-2-F5.0 CCZU-3-F 17.0 CCZU-5-F 5.0 CDU-2-F 11.0 CDU-3-F 12.0 CDU-5-F 7.0 Σ100.0

Example 34

Composition Conc./% Properties CCH-301 14.0 Transition T (S, N) < −30.0°C. CCH-501 11.0 Clearing point T (N, I) = +80.0° C. CCP-2F.F.F 10.0 Δn(589 nm, 20° C.) = +0.0607 CCP-3F.F.F 13.0 Δε (1 kHz, 20° C.) = +6.5CCP-5F.F.F 5.0 CCZU-2-F 5.0 CCZU-3-F 17.0 CCZU-5-F 5.0 CH-33 3.0 CH-353.0 CH-43 3.0 CCPC-33 3.0 CCH-3CF3 8.0 Σ 100.0

Example 35

Composition Conc./% Properties CC-5-V 14.0 Transition T (S, N) < −40.0°C. CCH-303 3.0 Clearing point T (N, I) = +76.0° C. CCH-501 5.0 Δn (589nm, 20° C.) = +0.0597 CCP-2F.F.F 10.0 Δε (1 kHz, 20° C.) = +5.5CCP-3F.F.F 12.0 V₁₀ (20° C.)= 1.80 V CCP-5F.F.F 4.0 V₉₀ (20° C.) = 4.44V CCZU-2-F 5.0 CCZU-3-F 16.0 CCZU-5-F 5.0 CCH-301 18.0 CH-33 2.0 CH-353.0 CH-43 3.0 Σ 100.0

Example 36

Composition Conc./% Properties CC-5-V 6.0 Transition T (S, N) = < −40.0°C. CCH-34 5.0 Clearing point T (N, I) = +75.0° C. CCH-301 18.0 Δn (5.89nm, 20° C.) = +0.0604 CCH-501 6.0 Δε (1 kHz, 20° C.) = +6.4 CCP-2F.F.F12.0 V₁₀ (20° C.) = 1.61 V CCP-3F.F.F 12.0 V₉₀ (20° C.) = 3.94 VCCP-5F.F.F 5.0 CCZU-2-F 6.0 CCZU-3-F 20.0 CCZU-5-F 5.0 CH-35 2.0 CH-453.0 Σ 100.0

Example 37

Composition Conc./% Properties CC-5-V 7.0 Transition T (S, N) < −30.0°C. CCH-301 5.0 Clearing point T (N, I) = +82.0° C. CCH-303 5.0 Δn (589nm, 20° C.) = +0.0630 CCH-501 14.0 Δε (1 kHz, 20° C.) = +8.0 CCP-2F.F.F12.0 V₁₀ (20° C.) = 1.69 V CCP-3F.F.F 12.0 V₉₀ (20° C.) = 4.08 VCCP-5F.F.F 4.0 CCZU-2-F 6.0 CCZU-3-F 22.0 CCZU-5-F 6.0 CH-33 2.0 CH-353.0 CH-45 2.0 Σ 100.0

Example 38

Composition Conc./% Properties CCH-303 11.0 Transition T (S, N) < −30.0°C. CCH-501 17.0 Clearing point T (N, I) = +83.5° C. CH-33 3.0 Δn (589nm, 20° C.) = +0.0624 CH-35 3.0 Δε (1 kHz, 20° C.) = +8.7 CH-45 3.0 γ₁(20° C.) = 151 m Pa s CCP-5F.F.F 3.0 V₁₀ (20° C.) = 1.51 V CCZU-2-F 6.0V₉₀ (20° C.) = 3.64 V CCZU-3-F 16.0 CCZU-5-F 6.0 CCPC-34 2.0 CDU-2-F10.0 CDU-3-F 12.0 CDU-5-F 8.0 Σ 100.0

Example 39

Composition Conc./% Properties CCH-301 19.0 Transition T (S, N) < −40.0°C. CC-5-V 17.0 Clearing point T (N, I) = +76.5° C. CCP-20CF3 6.0 Δn (589nm, 20° C.) = +0.0639 CCP-40CF3 6.0 Δε (1 kHz, 20° C.) = +5.2 CCP-2F.F.F11.0 γ₁ (20° C.) = 92 m Pa s CCP-3F.F.F 11.0 V₀ (20° C.) = 1.50 VCCP-5F.F.F 6.0 V₁₀ (20° C.) = 1.87 V CCP-20CF3.F 9.0 V₉₀ (20° C.) = 4.59V CCZU-2-F 5.0 CCZU-3-F 7.0 CCPC-34 3.0 Σ 100.0

Example 40

Composition Conc./% Properties CCH-301 20.0 Transition T (S, N) < −30.0°C. CC-5-V 16.0 Clearing point T (N, I) = +70.5° C. CCP-20CF3 6.0 Δn (589nm, 20° C.) = +0.0620 CCP-40CF3 5.0 Δε (1 kHz, 20° C.) = +7.4 CCZU-2-F5.0 V₀ (20° C.) = 1.23 V CCZU-3-F 8.0 V₁₀ (20° C.) = 1.52 V CCPC-34 4.0V₉₀ (20° C.) = 3.71 V CDU-2-F 12.0 CDU-3-F 14.0 CDU-5-F 10.0 Σ 100.0

Example 41

Composition Conc./% Properties CCH-3CF3 9.0 Transition T (S, N) < −40.0°C. CCH-5CF3 12.0 Clearing point T (N, I) = +80.0° C. CCH-302 10.0 Δn(589 nm, 20° C.) = +0.0633 CCP-2F.F.F 12.0 Δε (1 kHz, 20° C.) = +7.9CCP-3F.F.F 11.0 V₁₀ (20° C.) = 1.72 V CCP-5F.F.F 6.0 V₉₀ (20° C.) = 4.13V CCP-20CF3.F 3.0 CCZU-2-F 6.0 CCZU-3-F 14.0 CCZU-5F 6.0 CCPC-34 5.0CH-35 6.0 Σ 100.0

Example 42

Composition Conc./% Properties CH-33 4.0 Transition T (S, N) < −30.0° C.CH-35 3.0 Clearing point T (N, I) = +82.0° C. CCP-2F.F.F 10.0 Δn (589nm, 20° C.) = +0.0645 CCZU-2-F 6.0 Δε (1 kHz, 20° C.) = +11.2 CCZU-3-F16.0 V₁₀ (20° C.) = 1.35 V CCZU-5-F 6.0 V₉₀ (20° C.) = 3.26 V CDU-2-F9.0 CDU-3-F 11.0 CDU-5-F 8.0 CCH-3CF3 11.0 CCH-5CF3 9.0 CCPC-33 4.0CCPC-34 3.0 Σ 100.0

Example 43

Composition Conc./% Properties CCH-501 7.0 Transition T (S, N) < −30.0°C. CH-33 4.0 Clearing point T (N, I) = +81.0° C. CH-35 4.0 Δn (589 nm,20° C.) = +0.0624 CH-43 4.0 Δε (1 kHz, 20° C.) = +9.5 CCP-2F.F.F 12.0 γ₁(20° C.) = 180 m Pa s CCZU-2-F 6.0 V₁₀ (20° C.) = 1.34 V CCZU-3-F 16.0V₉₀ (20° C.) = 3.23 V CCZU-5-F 6.0 CDU-2-F 9.0 CDU-3-F 11.0 CDU-5-F 6.0CCS-3 8.0 CCS-5 7.0 Σ 100.0

Example 44

Composition Conc./% Properties CCH-301 14.0 Transition T (S, N) < −30.0°C. CC-5-V 5.0 Clearing point T (N, I) = +79.5° C. CH-33 3.0 Δn (589 nm,20° C.) = +0.0640 CH-35 3.0 Δε (1 kHz, 20° C.) = +9.7 CH-45 3.0 V₀ (20°C.) = 1.04 V CCP-2F.F.F 8.0 V₁₀ (20° C.) = 1.33 V CCZU-2-F 6.0 V₉₀ (20°C.) = 3.25 V CCZU-3-F 19.0 CCZU-5-F 6.0 CCPC-34 1.0 CDU-2-F 11.0 CDU-3-F12.0 CDU-5-F 9.0 Σ 100.0

Example 45

Composition Conc./% Properties ECCH-5CF3 21.0 Clearing point T (N, I) =+82.0° C. CC-5-V 5.0 Δn (589 nm, 20° C.) = +0.0654 CH-33 3.0 Δε (1 kHz,20° C.) = +8.5 CCP-2F.F.F 12.0 γ₁ (20° C.) = 165 m Pa s CCP-3F.F.F 12.0V₁₀ (20° C.) = 1.58 V CCP-5F.F.F 5.0 V₉₀ (20° C.) = 3.88 V CCP-20CF3.F6.0 CCZU-2-F 6.0 CCZU-3-F 20.0 CCZU-5-F 6.0 CCPC-34 4.0 Σ 100.0

Example 46

Composition Conc./% Properties CCH-303 11.0 Transition T (S, N) < −40.0°C. CCH-501 17.0 Clearing point T (N, I) = +84.5° C. CH-33 3.0 Δn (589nm, 20° C.) = +0.0628 CH-35 3.0 Δε (1 kHz, 20° C.) = +9.2 CH-45 3.0 V₁₀(20° C.) = 1.58 V CCP-5F.F.F 3.0 V₉₀ (20° C.) = 3.83 V CCZU-2-F 6.0CCZU-3-F 16.0 CCZU-5-F 6.0 CCPC-34 2.0 CEDU-3-F 15.0 CEDU-5-F 15.0 Σ100.0

Example 47

Composition Conc./% Properties CCH-501 7.0 Transition T (S, N) < −40.0°C. CH-33 3.0 Clearing point T (N, I) = +86.0° C. CH-35 3.0 Δn (589 nm,20° C.) = +0.0645 CH-43 3.0 Δε (1 kHz, 20° C.) = +10.2 CCP-2F.F.F 7.0V₁₀ (20° C.) = 1.44 V CCP-3F.F.F 5.0 V₉₀ (20° C.) = 3.44 V CCZU-2-F 6.0CCZU-3-F 15.0 CCZU-5-F 6.0 CDU-2-F 9.0 CDU-3-F 9.0 CDU-5-F 6.0 CCH-3CF37.0 CCH-5CF3 8.0 CCPC-34 3.0 CCPC-33 3.0 Σ 100.0

Example 48

Composition Conc./% Properties CCH-301 5.0 Transition T (S, N) < −40.0°C. CCH-501 16.0 Clearing point T (N, I) = +86.0° C. CCP-2F.F.F 12.0 Δn(589 nm, 20° C.) = +0.0622 CCP-3F.F.F 12.0 Δε (1 kHz, 20° C.) = +4.8CCP-5F.F.F 6.0 V₁₀ (20° C.) = 2.10 V CCP-20CF3 5.0 V₉₀ (20° C.) = 4.98 VCCP-40CF3 6.0 CCP-20CF3.F 9.0 CH-33 4.0 CH-35 3.0 CH-43 3.0 CH-45 3.0CCPC-34 4.0 CCH-3CF3 6.0 CCH-5CF3 6.0 Σ 100.0

Example 49

Composition Conc./% Properties CCH-5CF3 10.0 Transition T (S, N) <−30.0° C. CCH-34 5.0 Clearing point T (N, I) = +79.5° C. CC-5-V 16.0 Δn(589 nm, 20° C.) = +0.0650 CCP-2F.F.F 12.0 Δε (1 kHz, 20° C.) = +7.4CCP-3F.F.F 10.0 γ₁ (20° C.) = 113 m Pa s CCP-5F.F.F 7.0 V₁₀ (20° C.) =1.67 V CCP-20CF3.F 12.0 V₉₀ (20° C.) = 4.08 V CCZU-2-F 5.0 CCZU-3-F 16.0CCZU-5-F 5.0 CCPC-34 2.0 Σ 100.0

Example 50

Composition Conc./% Properties CCH-34  6.0 Transition T (S,N) < −40.0°C. CCH-3CF3  3.0 Clearing point T (N,I) = +75.0° C. CCH-5CF3  8.0 Δn(589 nm, 20° C.) = +0.0644 CCP-2F.F.F  11.0 Δε (1 kHz, 20° C.) = +10.1CCP-3F.F.F  10.0 V₁₀ (20° C.) = 1.42 V CCP-5F.F.F  6.0 V₉₀ (20° C.) =3.47 V CCP-20CF3.F  4.0 CCP-40CF3  8.0 CDU-2-F  10.0 CDU-3-F  12.0CDU-5-F  10.0 CCOC-3-3  4.0 CCOC-3-3  8.0 Σ 100.0

Example 51

Composition Conc./% Properties CCH-34  6.0 Clearing point T (N,I) =+81.0° C. CC-5-V  11.0 Δn (589 nm, 20° C.) = +0.0653 CC-3-2T  9.0 Δε (1kHz, 20° C.) = +7.7 CC-5-2T  9.0 V₁₀ (20° C.) = 1.70 V CCP-2F.F.F  11.0V₉₀ (20° C.) = 4.20 V CCP-3F.F.F  11.0 CCP-5F.F.F  6.0 CCP-40CF3  6.0CCP-20CF3.F  5.0 CCZU-2-F  6.0 CCZU-3-F  14.0 CCZU-5-F  6.0 Σ 100.0

Example 52

Composition Conc./% Properties CCH-34  5.0 Clearing point T (N,I) =+80.0° C. CC-5-V  8.0 Δn (589 nm, 20° C.) = +0.0642 CCH-3CF3  6.0 Δε (1kHz, 20° C.) = +7.8 CCH-5CF3  8.0 V₁₀ (20° C.) = 1.68 V CCP-2F.F.F  11.0V₉₀ (20° C.) = 4.08 V CCP-3F.F.F  11.0 CCP-5F.F.F  6.0 CCZU-2-F  6.0CCZU-3-F  14.0 CCZU-5-F  6.0 CCP-20CF3.F  8.0 CCP-40CF3  4.0 CCOC-4-3 5.0 CCOC-3-3  2.0 Σ 100.0

Example 53

Composition Conc./% Properties CCH-34  6.0 Clearing point T (N,I) =+79.5° C. CC-5-V  14.0 Δn (589 nm, 20° C.) = +0.0649 CCP-2F.F.F  11.0 Δε(1 kHz, 20° C.) = +9.5 CCP-3F.F.F  11.0 V₁₀ (20° C.) = 1.46 V CCP-5F.F.F 6.0 V₉₀ (20° C.) = 3.60 V CCP-20CF3.F  6.0 CDU-2-F  10.0 CDU-3-F  14.0CDU-5-F  10.0 CCOC-3-3  4.0 CCOC-4-3  8.0 Σ 100.0

Example 54

Composition Conc./% Properties CCH-34  6.0 Clearing point T (N,I) =+78.5° C. CC-5-V  15.0 Δn (589 nm, 20° C.) = +0.0652 CCH-5CF3  9.0 Δε (1kHz, 20° C.) = +9.4 CCP-2F.F.F  11.0 V₁₀ (20° C.) = 1.48 V CCP-3F.F.F 11.0 V₉₀ (20° C.) = 3.66 V CCP-5F.F.F  6.0 CCP-40CF3  4.0 CCZU-2-F  6.0CCZU-3-F  14.0 CCZU-5-F  6.0 DCZG-2-OT  4.0 DCZG-3-OT  4.0 DCZG-5-OT 4.0 Σ 100.0

Example 55

Composition Conc./% Properties CCH-34  5.0 Transition T (S,N) < −40.0°C. CC-5-V  8.0 Clearing point T (N,I) = +80.5° C. CCH-3CF3  6.0 Δn (589nm, 20° C.) = +0.0643 CCH-5CF3  8.0 Δε (1 kHz, 20° C.) = +7.8 CCP-2F.F.F 11.0 V₁₀ (20° C.) = 1.69 V CCP-3F.F.F  11.0 V₉₀ (20° C.) = 4.11 VCCP-5F.F.F  6.0 CCZU-2-F  5.0 CCZU-3-F  15.0 CCZU-5-F  5.0 CCP-20CF3.F 8.0 CCP-40CF3  5.0 CCOC-4-3  5.0 CCOC-3-3  2.0 Σ 100.0

Example 56

Composition Conc./% Properties CCH-34  5.0 Clearing point T (N,I) =+82.0° C. CC-3-2T  8.0 Δn (589 nm, 20° C.) = +0.0650 CC-5-2T  8.0 Δε (1kHz, 20° C.) = +6.5 CCH-5CF3  8.0 V₁₀ (20° C.) = 1.94 V CCP-2F.F.F  12.0V₉₀ (20° C.) = 4.71 V CCP-3F.F.F  11.0 CCP-5F.F.F  6.0 CCP-20CF3.F  12.0CCP-50CF3.F  6.0 CCP-40CF3  6.0 CCOC-4-3  8.0 CCG-(c3)m-F  10.0 Σ 100.0

Example 57

Composition Conc./% Properties CCH-34  5.0 Transition T (S,N) < −40.0°C. CC-5-V  6.0 Clearing point T (N,I) = +80.5° C. CCH-3CF3  6.0 Δn (589nm, 20° C.) = +0.0644 CCH-5CF3  8.0 Δε (1 kHz, 20° C.) = +7.9 CCP-2F.F.F 11.0 γ₁ (20° C.) = 124 m Pa s CCP-3F.F.F  12.0 V₁₀ (20° C.) = 1.65 VCCP-5F.F.F  5.0 V₉₀ (20° C.) = 4.06 V CCZU-2-F  5.0 CCZU-3-F  15.0CCZU-5-F  4.0 CCP-20CF3.F  10.5 CCP-40CF3  6.5 CCOC-4-3  4.0 CCOC-3-3 2.0 Σ 100.0

Example 58

Composition Conc./% Properties CCH-3CF3  8.0 Clearing point T (N,I) =+81.0° C. CCH-5CF3  5.0 Δn (589 nm, 20° C.) = +0.0655 CCH-301  9.0 Δε (1kHz, 20° C.) = +8.7 CCP-2F.F.F  8.0 V₁₀ (20° C.) = 1.56 V CCP-3F.F.F 13.0 V₉₀ (20° C.) = 3.77 V CCP-5F.F.F  5.0 CCZU-2-F  5.0 CCZU-3-F  8.0CCZU-5-F  5.0 CCP-30CF3.F  8.0 CCP-50CF2.F.F  8.0 CDU-3-F  9.0 CCOC-3-3 5.0 CPCC-2-3  4.0 Σ 100.0

Example 59

Composition Conc./% Properties CCH-3CF3  9.0 Transition T (S,N) = <−30.0° C. CCH-5CF3  7.0 Clearing point T (N,I) = +80.0° C. CCH-34  5.0Δn (589 nm, 20° C.) = +0.0652 CCP-2F.F.F  11.0 Δε (1 kHz, 20° C.) = +8.6CCP-3F.F.F  12.0 γ₁ (20° C.) = 144 m Pa s CCP-5F.F.F  5.0 V₁₀ (20° C.) =1.58 V CCP-20CF3  4.0 V₉₀ (20° C.) = 3.88 V CCP-30CF3  2.0 CCP-40CF3 7.0 CCP-20CF3.F  10.0 CCZU-2-F  5.0 CCZU-3-F  15.0 CCZU-5-F  4.0CCTTCC-5-5-5-5  4.0 Σ 100.0

Example 60

Composition Conc./% Properties CCH-34  6.0 Transition T (S,N) = < −40.0°C. CCH-501  8.0 Clearing point T (N,I) = +80.0° C. CCH-5CF3  8.0 Δn (589nm, 20° C.) = +0.0656 CCP-2F.F.F  11.0 Δε (1 kHz, 20° C.) = +8.4CCP-3F.F.F  11.0 V₁₀ (20° C.) = 1.57 V CCP-5F.F.F  6.0 V₉₀ (20° C.) =3.89 V CCP-40CF3  8.0 CCP-20CF3.F  10.0 CCZU-2-F  6.0 CCZU-3-F  14.0CCZU-5-F  6.0 CHO-3CF3  6.0 Σ 100.0

Example 61

Composition Conc./% Properties CCH-34  6.0 Transition T (S,N) = < −40.0°C. CCH-501  10.0 Clearing point T (N,I) = +80.0° C. CCH-5CF3  6.0 Δn(589 nm, 20° C.) = 0.0653 CCP-2F.F.F  11.0 V₁₀ (20° C.) = 1.41 VCCP-3F.F.F  11.0 V₉₀ (20° C.) = 3.45 V CCP-5F.F.F  6.0 CCP-20CF3.F  8.0CCZU-2-F  6.0 CCZU-3-F  14.0 CCZU-5-F  6.0 DCZG-2-OT  4.0 DCZG-3-OT  4.0DCZG-5-OT  4.0 CCOC-3-3  4.0 Σ 100.0

Example 62

Composition Conc./% Properties CC-5-V  18.5 Clearing point T (N,I) =+70.0° C. CCH-303  6.0 Δn (589 nm, 20° C.) = 0.0650 CCH-501  6.0 V₁₀(20° C.) = 1.56 V CCP-2F.F.F  12.0 V₉₀ (20° C.) = 3.93 V CCP-3F.F.F 13.0 CCP-5F.F.F  5.0 CCP-20CF2.F.F  10.0 CCP-30CF2.F.F  10.0 CCZU-2-F 5.0 CCZU-3-F  10.0 PCH-7  4.5 Σ 100.0

Example 63

Composition Conc./% Properties CCH-301  11.5 Transition T (S,N) = <−30.0° C. CCP-2F.F.F  10.0 Clearing point T (N,I) = +80.0° C. CCP-3F.F.F 13.0 Δn (589 nm, 20° C.) = 0.0653 CCP-5F.F.F  5.0 γ₁ (20° C.) = 161 mPa s CCZU-2-F  5.0 V₁₀ (20° C.) = 1.54 V CCZU-3-F  16.0 V₉₀ (20° C.) =3.76 V CCZU-5-F  4.0 CCP-20CF2.F.F  5.0 CCP-30CF2.F.F  6.0 CCP-50CF2.F.F 6.0 CH-33  3.0 CH-35  2.0 CH-43  2.5 CCH-3CF3  7.0 CCH-5CF3  4.0 Σ100.0

FIGURES

FIG. 1 shows the principle of construction of a liquid-crystal switchingelement according to the invention having crossed polarisers.

FIG. 1a) shows the arrangement of the most important constituents of theswitching elements of the first preferred embodiment and the ray path inside view.

BL: denotes backlighting, P: denotes polariser or analyser (thetransmission direction is denoted by the respective bars), z: denotesthe normal to the display surface, n∥: denotes the preferentialdirection of the liquid-crystal director in the centre of the layerbetween the substrates (not shown), corresponds to the direction of theextraordinary refractive in- dex (n_(o)), and n⊥: denotes the directionperpendicular to the preferential direc- tion of the liquid-crystaldirector in the centre of the layer between the substrates (in thex-axis and in the z-axis), cor- responds to the direction of theordinary refractive index (n_(e)).

FIG. 1b) shows a plan view of the alignment of the relevant axes. Thesymbols from FIG. 1a are also used here, where appropriate.

FIG. 2 shows the definition of the observation angles in the plane ofthe display (Φ and Φ′) and perpendicular to the normal (Θ).

FIG. 3 shows the transmission through the arrangement shown in FIG. 1,but with the angle of the polariser to the 2nd polariser Ψ_(PP) beingvaried. The optical retardation (d·Δn)_(LC) was 277 nm.

FIG. 4 shows the transmission voltage characteristic line of aliquid-crystal switching element according to the invention in normallyblack mode in accordance with Example 1. The parameters are as indicatedin the text. Two curves are shown which were obtained for two differentcells with identical results in each case. The curves were obtained forΘ=0° and for Θ=30° and Φ=45°.

FIG. 5 shows, similarly to FIG. 4, the characteristic lines of aliquid-crystal switching element, but here of a TN switching elementhaving d·Δn of 0.5 μm (corresponding to the 1st Gooch and Tarry minimum)of Comparative Example 1. The curve shows the results for two differentcells at Θ=0°.

FIG. 6 shows the characteristic line of a TN switching element havingd·Δn of 0.50 μm in comparison with that of a switching element accordingto the invention, both with virtually the same capacitive threshold,also known as the Freedericks threshold, at an observation angle ofΘ=10°, Φ=45°.

FIG. 7 shows the wavelength dependence of the transmission of theliquid-crystal switching element according to the invention from Example1 (continuous curves) in comparison with that of a TN display havingd·Δn=0.50 μm from Comparative Example 1 (dashed curves). The three setsof curves correspond to the addressing voltages for 10, 50 and 90%relative contrast.

FIG. 8 shows in two parts the isocontransmission curves of twoliquid-crystal switching elements. The display in polar coordinates wasselected here, as defined in FIG. 2. The transmission was determined foreach point in the hemisphere above the liquid-crystal switching elementwith a fixed addressing voltage which results in a minimum transmissionof 10%. Points of equal transmission are connected by isotransmissionlines. The isotransmission lines are staggered at separations of 10%absolute in each case. Areas having a transmission in the region of thesame multiple of 10% are characterised by the same grey shade. Thedarkest region corresponds to a transmission of from 0% to 10%,inclusive, the next grey region from more than 10% to 20% inclusive, thepale grey region from more than 20% to 30% inclusive, and so on. Theother regions are not shaded in grey.

FIG. 8a) shows the results for Comparative Example 1.

FIG. 8b) shows the results for the liquid-crystal switching elementaccording to the invention from Example 1.

FIG. 9 shows in three parts the isocontrast curves for three differentswitching elements. As in FIG. 8, polar coordinates were used. All threesets of isocontrast curves were obtained for addressing with twovoltages which correspond to the two characteristic voltages V₁₀ and V₉₀for the respective switching element. The curves connect points of thesame contrast ratio. The contrast ratios decrease successively towardthe outside, starting with the shortest, closed curve. The preferredquadrant having the highest contrast ratio at Φ=45° (corresponds to315°) is at bottom right in the figure.

FIG. 9a) shows the results for the switching element according to theinvention from Example 1. The individual curves stand from the insideoutward successively for contrast ratios of 7, 5, 3, 2 and 1.

FIG. 9b) shows the results for the switching element according to theinvention from Example 2. The individual curves stand from the insideoutward successively for contrast ratios of 7, 5, 3 and 2.

FIG. 9c) shows the results for the TN switching element from ComparativeExample 1. The individual curves stand from the inside outwardsuccessively for contrast ratios of 10, 7, 5, 3, 2 and 1.

What is claimed is:
 1. A liquid-crystal switching element comprising: aliquid-crystal layer, between two parallel substrates, having an initialalignment which is essentially parallel to the substrates and isessentially untwisted, wherein the layer has an optical retardation[(d·Δn)_(LC)] of from 0.07 μm to 0.17 μm. at least one polarizer, adevice for generating an electric field, which is aligned essentiallyparallel to the substrates in the case of a liquid-crystal layer ofnegative dielectric anisotropy and is aligned essentially perpendicularto the substrates in the case of a liquid-crystal layer of positivedielectric anisotropy, and, at least one birefringent layer, which iseither a λ/2 saver or two λ/4 layers, wherein the optical retardation ofthe birefringent layer or of the birefringent layers [(d·Δn)_(BL)] iseither essentially half or essentially twice the optical retardation ofthe liquid-crystal layer.
 2. A liquid-crystal switching elementaccording to claim 1, which comprises at least one linear polarizer. 3.A liquid-crystal switching element according to claim 1, wherein theliquid-crystal layer has a twist angle (φ) in the range from −25° to+25°.
 4. A liquid-crystal switching element according to claim 1,wherein the optical retardation of the liquid-crystal layer is or can beswitched from its initial value to essentially 0 nm.
 5. A liquid-crystalswitching element according to claim 1, which is a transmissive ortransflective liquid-crystal switching element.
 6. A liquid-crystalswitching element according to claim 1, wherein the optical retardationof the liquid-crystal layer is from 0.12 μm to 0.16 μm.
 7. Aliquid-crystal switching element according to claim 1, wherein theliquid-crystal layer has a twist angle (φ) of from −10° to +10°.
 8. Aliquid-crystal switching element according to claim 1, wherein theoptical retardation of the liquid-crystal layer in the fully switchedstate is from 0 nm to 80 nm.
 9. A liquid-crystal switching elementaccording to claim 1, wherein the liquid-crystal layer has positivedielectric anisotropy.
 10. A liquid-crystal switching element accordingto claim 1, wherein the element is capable of operating in normallywhite mode.
 11. A liquid-crystal switching element according to claim 1,which is a reflective liquid-crystal switching element.
 12. Aliquid-crystal switching element according to claim 1, which is atransmissive liquid-crystal switching element.
 13. A liquid-crystalswitching element according to claim 1, wherein the liquid-crystal layerhas negative dielectric anisotropy.
 14. Electro-optical liquid-crystaldevice, which comprises a liquid-crystal switching element or aplurality of liquid-crystal switching elements according to claim
 1. 15.Electro-optical liquid-crystal display device according to claim 14,which contains a multiplicity of liquid-crystal switching elements, andthese are arranged in matrix form.
 16. Electro-optical liquid-crystaldisplay device according to claim 14, wherein the liquid-crystalswitching elements are addressed by means of a matrix of activeelectrical switching elements.
 17. A liquid-crystal switching elementaccording to claim 1, wherein the birefringence of the liquid-crystallayer is from 0.02 to 0.09.
 18. A liquid-crystal switching elementaccording to claim 1, wherein the layer thickness of the liquid-crystallayer is from 0.05 to 7 μm.
 19. A liquid-crystal switching elementaccording to claim 1, wherein the layer thickness of the liquid-crystallayer is from 1.5 to 4 μm.
 20. A liquid-crystal switching elementaccording to claim 1, wherein the liquid-crystal layer has a temperaturerange of the nematic phase at least encompassing −20° C. to 60° C.
 21. Aliquid-crystal switching element according to claim 1, wherein theswitching element has a sum response time for switching between V₁₀ andV₉₀ and back of at most 100 milliseconds.
 22. A liquid-crystal switchingelement according to claim 1, wherein the switching element has a sumresponse time for switching between V₁₀ and V₉₀ and back of at most 80milliseconds.
 23. A liquid-crystal switching element according to claim1, wherein the switching element has a sum response time for switchingbetween V₁₀ and V₉₀ and back of at most 50 milliseconds.